Help! My copper bar isn't flat!

[Gooserider]

A week or two ago, I bought a big hunk of copper bar from my local surplus metals dealer ($2.80 / lb) This bar was 3/4" x 2.25" x ~2', (20mm x 58mm x ~600mm) and I cut a couple peices off it about 3.125" (78mm) long to use in making waterblocks for my dual Athlon mobo. I was quite suprised to find both peices and the remainder of the bar have a 'cup' across the 2.25" dimension. One surface is slightly concave, the other convex by what looks like the same amount. Good news is they appear flat in the other dimension.

I don't have an exact dimension on the degree of the cup, but if I hold a straight edge accross it, it looks like about .010 to .030 gap in the center.

Is this normal, or did I get stuck with a bad hunk of copper?

Is it flattenable? If so, what is the best time and method to do so?

I could attempt to fly cut and / or lap the surface flat now, or wait until after the block is milled, or even milled and assembled and do whatever flattening is needed then.

Tool resources available include a Smithy (TM) combination lathe / mill setup, which is not all that great. However my machinist skills are worse, this is my first real precise machining project, up until now I've just hacked at things by eye.

My plan was to mill my water passages into the 3/4" block, leaving about 3/16 (4mm) thickness on the bottom, with about a 50/50 ratio between water passages and 'interference pins' (each about 1/8" wide) over the core area. The top would be 1/4" thick, and contain the barbs. It will use a clip on mount, not a bolt through. The top will be attached by soldering it to the bottom.

Is there any reason to change this?

If I were working in wood, I would probably cut the design into the hollow side of the cup, put everything together, and flatten it as the last step. Is this a good plan for working in copper? I am somewhat afraid that if I flatten it now, I'll get more distortion later, and need to flatten it again then.

I know there are several machinists that read this forum, I really feel a need for advice if you can give it.

Thanks,

Gooserider

[MadDogMe]

I don't think it's evr 'flat', though some are better than others probably. If I were you I'd fly cut both sides before you machined it anyway. Or at the least the side that's going to be the base to provide a good bottom to machine the top from (so it does'nt 'see~saw')...

There's no reason it'll 'distort' again. The shape is from the manufacturing process, not anything that happened after...

[bigben2k]

Originally posted by MadDogMe
I don't think it's evr 'flat', though some are better than others probably. If I were you I'd fly cut both sides before you machined it anyway. Or at the least the side that's going to be the base to provide a good bottom to machine the top from (so it does'nt 'see~saw')...

I think that would be good advice, for a carpenter.

Given the difference, I think I'd opt to lap it after it's machined.

[Cathar]

Fly-cut both sides.

Then machine it.

Then lap it after it's machine.

The heat and stresses of the machining will cause the copper to bend slightly (in the order of a small number of microns), but enough to require lapping again after machining.

[N8]

Originally posted by Cathar
Fly-cut both sides.

Then machine it.

Then lap it after it's machine.

The heat and stresses of the machining will cause the copper to bend slightly (in the order of a small number of microns), but enough to require lapping again after machining.

Yes, this is the way I would recommend as well.

[jaydee]

Originally posted by Cathar
Fly-cut both sides.

Then machine it.

Then lap it after it's machine.

The heat and stresses of the machining will cause the copper to bend slightly (in the order of a small number of microns), but enough to require lapping again after machining.

Thats the way I would do it to. That way the peice can sit flat in the vise or on the table and your depths will be consistant on the design.

MadDogMe was pretty close except for the last part. The metal will distort again if the design being milled into it causes heat build up. The parts that are thinner will warp a little tweaking the whole peice, but not much. When copper, or any metal really, is roled into a flat bar it is always concaved in the middle more so than the outer sides and if it was in a sheet form then it is going to have all kinds of humps and drops in it. Just the way it is made. Google for metal manufacturing and you should be able to see why.

[Gooserider]

Four out of five responses said to fly cut it flat first.

(Note to self, next time buy a thicker bar so there is more room for flycutting... This may be a bit tight by the time I get both sides flat...)

Now all I have to do is get a lathe collet big enough to hold one of my larger flycutters so I can do the whole block in one pass. One of the worst things about my Smithy is that the mill head uses an MT-3 taper instead of an R-8. Makes it a real pain and much more expensive to find tooling.

I don't think I'll have to much trouble with heat related distortion, I've set up the machine with a coolant pump using a soluble oil stream. Yesterday when I was fly cutting the rough cut end of the block I found the coolant kept things cool enough that I didn't feel any heat even putting my finger on the cut surface right after a pass. (What I haven't figured out real well is how to keep the cutter from giving everything within five feet a soluble oil shower. I've hacked up a partial crude solution involving hanging cut up laundry soap bottles arround the mill head, but it's a real kludge and only partially effective.)

I do thank everyone for their advice.

Gooserider

[N8]

If your bar is 3/4" thick, I wouldn't worry too much about losing thickness by flycutting both sides. I don't think you would need to lose much more than 0.01 - 0.03" getting your bar flat on each side unless it was really warped. That is not much in comparison to the 3/4" thickness.

I would just flycut a smaller piece that you have already cut off instead of the whole length to see how much is really necessary to take off.

If you don't want to deal with flycutting, take one of the cut pieces and sand it with 220 grit SiC sandpaper and water or even a stationary belt sander (if you have one) to get it pretty flat before machining.

You want to true it up before machining any O-ring grooves or channels into it. Flycutting would be fastest and best, but this also depends on your equipment and experience.

[Gooserider]

[quote]N8 If your bar is 3/4" thick, I wouldn't worry too much about losing thickness by flycutting both sides. I don't think you would need to lose much more than 0.01 - 0.03" getting your bar flat on each side unless it was really warped.[quote]
I don't know... It looks pretty badly warped. I've got two hunks cut off that are going to be the blocks. If I put them together so the concave sides are facing, on the edges it looks like about a 1/16" gap in the middle. If I put the convex faces are together it is a big rock. The other test I did is that I have one of those pocket steel rules with a sliding pocket clip on it with ears like a depth gauge. If I pull the clip off, and use the ruler to bridge the high spots, the ear on the clip goes under it easily in the center. ;(

I'm guessing I'll have to get rid of at least .05" on each side. Still not a huge amount, but...

That is not much in comparison to the 3/ 4" thickness. I would just flycut a smaller piece that you have already cut off instead of the whole length to see how much is really necessary to take off.

That's what I was planning - I figure don't mess with the big hunk till I know what I'm going to do with it. I wouldn't want to mess with the big chunk until I chop it up anyhow since it's currently longer than either axis on my Smithy.

If you don't want to deal with flycutting, take one of the cut pieces and sand it with 220 grit SiC sandpaper and water or even a stationary belt sander (if you have one) to get it pretty flat before machining. You want to true it up before machining any O-ring grooves or channels into it. Flycutting would be fastest and best, but this also depends on your equipment and experience.

Well, I figure I won't learn flycutting or other machining skills unless I actually do them, so I've got to get on it. I have a hand held belt sander, but I don't know how true it is, nor do I think it would be happy to have me sanding copper and potentially getting little copper bits in its innards :shrug:

My skills are beginner level, and my equipment isn't very good by todays standards, but I think it's adequate for the task. When I was facing off my cut ends, I had lots of problems with my setup initially, but once I got everything debugged, the ends looked pretty good. Of course I was wanting to have the blocks be 80mm long, cut them (with a Sawz-All) to about 81-82mm, and ended up at 78mm, but that's a different story....

I think my planned design is also going to be fairly tolerant of most everything except the lapping. I'll be soldering the block together so I don't need to worry about O-rings, and the top / bottom fit only needs to be fairly close. I'm going to be cutting my water channels as close to the bottom as I can get away with (my target is 3-4mm base thickness) but that gives me enough room that if I'm off a bit it won't hurt anything.

All in all, I think I have something that will do a good job, but be pretty tolerant about how perfect I get everything in building it.

Gooserider

[MMZ_TimeLord]

Everyone has got it nailed... flycut and/or machine the raised side first to level it out... then the cupped side.

Just a note about your mill... if you don't have a collet to fit your fly cutter you can use a 3 or 4 flut endmill that is quite wide. like 3/4" or 1" and do several passes with your table. Just lock the mill head at the height you want to take off a few thousandths and make 2 or 3 passes. Then lower it another few thousandths if you haven't gotten it all.

Finally ... lap it for a nice finish.

I'm not completely familiar with machining terms... but I have a mill (in storage.. ) that I used on my blocks.

The raw copper I got came with the same slight bow to it and that's how I corrected mine.

[Gooserider]

MMZ_TimeLord Everyone has got it nailed... flycut and/or machine the raised side first to level it out... then the cupped side.

Thanks, especially for the mention of the sequence of which side to do first.

Just a note about your mill... if you don't have a collet to fit your fly cutter you can use a 3 or 4 flut endmill that is quite wide. ...

Well I hope to have gotten that taken care of - I just visited one of the local used machine places, and picked up a few things, including a 1/2" collet. (previously my largest was a 3/8") I'll have to double check, but I think my widest 1/2" flycutter will go wide enough to do the block in one pass.

I am getting to really be annoyed with this Smithy mill-drill machine, it seems they don't do anything with standard tooling - The millhead uses MT-3 taper instead of R-8, so finding tooling is either expensive or difficult. (R-8 is one of the major industry standards, and tooling for it is easy to find and comparatively inexpensive.) However I am managing to get my tooling collection built up some, to the point where I might be able to do something useful with it.

Finally ... lap it for a nice finish. I'm not completely familiar with machining terms... but I have a mill (in storage.. ) that I used on my blocks. The raw copper I got came with the same slight bow to it and that's how I corrected mine.

I noticed that when I was doing multiple passes before on the cut ends of my blocks that I was getting a line between the passes - I couldn't feel it, but it was very visible - is this normal, and is it something to worry about, or will the lapping get rid of it?

[MMZ_TimeLord]

Yeah, it's pretty standard to see a line on the second pass... if you leave the mill head locked and do another two passes the line should almost disappear. This is due to the cutting heads feed rate. Not all the material you want removed will happen in one pass.

If you had to make two passes on the surface to get it all. Make the same two again WITHOUT changing your mill head hight.

It will smooth up the surface and some of the swirling will disappear.

You should then be able to lap the rest of the milling marks out and get a mirror finish.

Just check what BladeRunner has done...

[Gooserider]

Well, I've started cutting. After the better part of two days setup and repairing the Smithy, and more setup, and repairing the Smithy again, etc. I have almost gotten the
two blocks fly cut.

I'm also just about ready to see if anyone has gotten the DNS registrations on 'Smithys_suck.com' or equivalent...

I've had to fix the drive nut on the crossfeed table twice so far, it keeps coming out of the socket in the table.

I've discovered that in addition to non standard mill head collets, it has a non-standard mount for the lathe chuck.

It seems that the same amount of movement registered on the mill depth indicator dial does NOT translate to the same amount of change in the mill head itself. (Note that much interpolation is required, the finest gradient on the depth dial is .040", I was wanting about a 10th of that...)

The lock on the main feed table hits the underside of the crossfeed table before it completely locks the main table. To lock the main table down tight, it is necessary to take the lock handle out, substitute a smaller screw, and tap the lock tight with a hammer.

Some of the assorted screws that hold the cranks on like to fall out from vibration.

If one attempts even a TINY cut with the flycutter, the millhead vibrates up and down visibly every time the cutter goes around. (I've got the flycutter set to about 64mm, traversing the block which is about 60mm wide. The cutter is turning @ 1380 RPM, and I'm using a very low feed speed on the table drive. Not sure just what the IPM rate is, but it takes about 10 minutes to go from clear of the 80mm block on one end to clear of the block on the other)

The first block ended up mostly smooth and flat, on each side, except for some gouges. For some reason the cutter seems to leave 99% of the block smooth. But it cuts a couple of arcs on each pass, I think where the outside swing of the bit goes on or off the block. I decided that the scratches didn't appear to be in the die area, so I think I can live with them.

Of course one side was about .745" thick and the other was about .710"... Who said the two sides needed to be parallel?

This was probably not the Smithy's fault however. I'm using a cheap asian mfg. (from Harbor Freight Tools) drillpress vise to hold the blocks. Since I need to be able to get the entire face, I can't use hold down clamps. I think the vise jaw is lifting up when I clamp down on the vise. The second block was showing .748" vs. 718" when I did the first side, so I put the fat edge on the side I think lifts up. Hopefully when I get the second side done it will have taken more off that side so I'll end up with sort of uniform thickness, even if it isn't at right angles to the sides.

On the bright side, I should be much cleaner now. <NOT!> I've done the best I can with making shields, but I still get this nice shower of soluble oil coolant. (BTW, I've been told that the coolant gets old and stinks after a while, what is the best way to get rid of it when it does?)

I'm really getting to hate this Smithy peice of $#!^, what's worse, the used machine place I've just started getting some stuff at says they could have sold me a used BRIDGEPORT for what I paid...

Gooserider

[MMZ_TimeLord]

Damn dude... that blows.

Seems like you have it under control... Keep plugging away.

BTW... .03" is not too bad to be able to even up. Your vice probably is shifting on each pass.

One thing to try is run a pass and then move the table so the block passes around the mill head, then run the second pass (other half of the block). It SHOULD keep the vice shifting even on both halves of the block (both cuts made in the same direction) and therefore your face should be even within a few thousanths.

As to the coolant, you have me there... I milled mine dry. I know, shame-shame, but it worked fine. The end mills I was using were dirt-cheap so I could afford to dull them down.

[Gooserider]

Well, I made a bunch more passes today, seems like it kept getting worse, not better. I tried upping the mill speed to 3,000RPM, part of the cut was beautiful, part looked like a steel wool pad. I tried lowering the speed, that didn't help either.

I tried making multiple passes with the mill head at the same height. It helped some, but not much. After 3-4 passes, I couldn't see that the flycutter was taking off any more material, but the surface would still be rough. I'd then lower the cutter the smallest amount I could, and repeat, with much the same results.

Finally I put a coat of Dykem on the block to see what kind of cutting pattern I was getting. I found the back of the cutter was cutting, but the front side wasn't! The pattern was also not uniform accross the entire surface. But this pass didn't have any marks that were to terrible, so I decided to call it quits. The other side isn't to bad, so I'm going to use this side for milling the pattern into, and the side I did earlier for the CPU contact surface. Hopefully I'll be able to get if flat enough when I lap the block. (The Dykem Blue will be reall handy for that.)

The downside is that I took a LOT of material off, the current thickness of this block is between .690" and .705" (originally over .750") But the thickness is more uniform than that of my first block, even if the sides are not perpendicular to the faces. I'm NOT happy with the way these blocks are turning out so far, but I think I'll be able to deal with it.

At least from this point on, I'll be able to work with hold down clamps instead of that cheap vise, so perhaps I'll have better control on the rest of the project.

Gooserider

[bigben2k]

Hmmm... seems like your table isn't level, or your drilling head isn't perfectly vertical. Is it badly off?

I know you've got a few problems with the tool itself, from what you've stated. The most obvious thing that comes to mind, is that your mounting rig (where you put the block) has to be perfectly clean. Is it?

You can use a locking washer, to help prevent those screws from coming loose from vibrations.

Good luck with the hold down clamps: it looks more promising.

[MMZ_TimeLord]

Two things...

One: Your mill head shaft is not at 90° to the table surface. This is causing your milling head to cut only on the back half.

Solution one: See if there is an adjustment on the table or mill head neck to adjust the angle. Get out a carpenters square (big one... 18" on a side at least) and adjust the head shaft to 90°.

If there is no adjustment, I don't know how to correct it unless your table is bolted to the frame of the mill. If so, you MAY be able to shim the table to compensate.

Two: Your feed rate could be too fast. Are you using an electric feed motor or manual crank?

Solution Two: If you are using a motor, see if you can lower the feed rate.

If you are using a hand crank, try and half your RPM when turning.

Hope this all helps...

[Gooserider]

bigben2k: Hmmm... seems like your table isn't level, or your drilling head isn't perfectly vertical.

Well, I thought it was... my initial checks seemed to say that it was OK, but I don't have the worlds most accurate tools.

The most obvious thing that comes to mind, is that your mounting rig (where you put the block) has to be perfectly clean. Is it?

As far as I can tell, my mounting surfaces have been as clean and dirt free as I can get them.

You can use a locking washer, to help prevent those screws from coming loose from vibrations.

I may try that, or Blue Locktight, assuming I can FIND the damn screws... Lock washers will be a problem on some of them as they are recessed screws, but I'm sure I can get them with Locktight.

Good luck with the hold down clamps: it looks more promising

That's what I'm hoping. I know that part of my problem with the flycutting was that my vise lifted the part up when I clamped on it. I figure if I use hold down clamps at least the blocks won't be able to move.
---------------

MMZ_TimeLord: Two things... One: Your mill head shaft is not at 90° to the table surface. This is causing your milling head to cut only on the back half.

Makes sense, It's what I was starting to suspect when I saw the cutting pattern.

Solution one: See if there is an adjustment on the table or mill head neck to adjust the angle.

There is no documented adjustment according to the manual...

Get out a carpenters square (big one... 18" on a side at least) and adjust the head shaft to 90°. If there is no adjustment, I don't know how to correct it unless your table is bolted to the frame of the mill.

The challenge with that is that there isn't really a place to measure against. There is a big flange around the bottom of the mill quill, so I can't get straight on that shaft. Before I found what a peice of .... this thing is, I would have assumed that the quill was parallel to the side of the head, but these days I'm not putting bets on it.

The only adjustment that I can see is a hairy one. There is a big block bolted on top of the lathe head. The block has a column sticking out of it that the mill head slips over (The mill head resembles a drill press head on steroids) Possibly I could slide the mill head up the column far enough to unscrew the bolts holding the column block on, and stick some shims under it. Possible, but it would really be a B!^C# to do, and I don't know if it would cure my problem.

At least I'm at the point now where I'll be using mill bits, and I don't think there will be a need to be quite so fussy. The measurements inside the block have a bit of flex to them in so I'm not to worried about a few thousandths here and there long as I don't poke through a wall or the bottom of the block.

If so, you MAY be able to shim the table to compensate. Two: Your feed rate could be too fast. Are you using an electric feed motor or manual crank?

Neither, sort of... The way my model Smithy works is that there are two motors, one for the mill head, and one for the lathe. The mill head motor just spins the mill bit; the lathe motor spins the lathe and drives the power feeds on both the X & Y table axiis (as needed for making screw threads, etc.) I was run the mill motor for the flycutter, and the lathe motor for table movement.

The lathe uses a change gear box, and a 3 speed gear selector. I am using the slowest spindle speed (160RPM)
and the lowest speed gear set, giving me the following speed options: (I/R = Inches/rotation, I/M = Inches/min, M/R mm/rotation, M/M mm/minute)

Gear...I/R...I/M.....M/R....M/M
..L.. .002". .320". .05mm.. 8mm
..M.. .004". .640". .10mm.. 16mm
..H.. .008". 1.28". .20mm.. 32mm

When I've been doing my cuts, I mostly use L speed, which seems pretty darn slow to me, it takes about 10-15 minutes to go from clear on one side of the 80mm block to clear on the other. I had trouble at times even seeing the table moving.

In concept the Smithy type multi function machine is a neat idea. Take a lathe, turn the tool rest into a table, and put a mill head over it. Get the function of your two most important metal working tools in the floor space of one. Unfortuneately, it seems the implementation is lacking.

Solution Two: If you are using a motor, see if you can lower the feed rate. If you are using a hand crank, try and half your RPM when turning. Hope this all helps...

The speed I'm using now is as low as it gets, I think my problem is more the tilt on the mill head than anything else. However I'll probably be scribing the layout for my blocks on the rougher side of each one tonight and starting to mill the passages tomorrow, something I expect to be less critical.

I also think this machine may end up on E-bay before to long...

Gooserider

[iggiebee]

The process of making the head of the mill completly perpendicular to the table, involves several steps, and is called "tramming" or "squaring the head". There are various procedures and instruments to do this; a little Googling will find you related web pages.

Here is one example

[Gooserider]

iggiebee: The process of making the head of the mill completly perpendicular to the table, involves several steps, and is called "tramming" or "squaring the head". There are various procedures and instruments to do this; a little Googling will find you related web pages. Here is one example

Nice example, I hadn't seen the process before, though I had expected it to look something like that.

Of course I thought it amusing the way they so casually said to adjust out the error, since I don't know of an official adjustment of any sort on the Smithy, and the only way I've guessed at from looking at the unit would involve measuring, guessing at a shim value, partial dissassembly and shimming, then putting everything back and trying it again.... NOT FUN... At least for now I have started milling the channels, which I see as less critical about head tilt than the flycutting was. I just need to be sure not to mill through any walls and ruin the block. (I also wish I could mill more than .080" at a pass, it gets old when you are trying for about .5" total...)

Minor question, my milling book talks about 'up milling' vs. 'down milling' and how one should only do 'up milling'. The pictures show a cutter milling one edge of a workpiece, and I get the difference in that situation. What I'm mostly doing however is milling channels into a block where the material is going into the cutter, and so the cutter is surrounded by material in the entire 180* of the direction of travel. In that case, it seems to me like half the material is being fed as in 'up milling' and half as in 'down milling', and I was wondering if it actually made any difference which way one travelled when making a channel. (Once you start widening it, then there is a difference, but not on the original cut...)

Gooserider

[iggiebee]

Minor question, my milling book talks about 'up milling' vs. 'down milling' and how one should only do 'up milling'. The pictures show a cutter milling one edge of a workpiece, and I get the difference in that situation. What I'm mostly doing however is milling channels into a block where the material is going into the cutter, and so the cutter is surrounded by material in the entire 180* of the direction of travel. In that case, it seems to me like half the material is being fed as in 'up milling' and half as in 'down milling', and I was wondering if it actually made any difference which way one travelled when making a channel. (Once you start widening it, then there is a difference, but not on the original cut...)

Sorry, when posting the tip for squaring the head of the mill didn't mean to come across as an expert geek, I have a small cnc milling machine, with a cad/cam program that figures most of the stuff for me, and I am also learning the ropes so to speak. I am sure there are better qualified people here, in this forum that will better answer your question, OR will dutifully and instantly correct any barbarisms you or I can make

Assuming when you mention the"cutter" that you are referring to an "end mill", and not to a "cutter wheel", my guess for the "up milling" or "down milling" is that you should cut the material always in the direction of the rotation of the quill (up milling), so the sharp edges of the tool will be "biting", not back-sliding against the material beingt cut.

Hope this of help.

[Gooserider]

iggiebee: Sorry, when posting the tip for squaring the head of the mill didn't mean to come across as an expert geek, I have a small cnc milling machine, with a cad/cam program

No offense intended, I appreciated the tip, it was just my sense of irony comparing the way the description made it sound so easy compared to the difficult task it appears to be with the Smithy.

Some ways you may be ahead of me, my machine doesn't have CNC, or even position readouts beyond the handle calibrations. I do have power feed of a sort, but it's limited. Makes it a real challenge to try and see where you are in the process of making a cut while dodging the coolant being splattered by the mill bit.

Assuming when you mention the"cutter" that you are referring to an "end mill", and not to a "cutter wheel", my guess for the "up milling" or "down milling" is that you should cut the material always in the direction of the rotation of the quill (up milling), so the sharp edges of the tool will be "biting", not back-sliding against the material beingt cut.

Yes, I was talking about an end mill, not a cutting wheel. I agree with what you are saying, and it seems pretty obvious when cutting along an edge which direction one should go, since only one side of the end mill is contacting the material. But when you are doing what I am, which is boring into the material, and then moving sideways, it isn't so obvious. It seems to me that the material will always be surrounding the mill bit the same way no matter what direction one cuts.

Gooserider

[Zymrgy]

I have never heard the terms "up milling" or "down milling", but I am sure they are talking about the difference between what I call climb mill vs conventional milling, as shown---

(edit...wow, bad pics try this
http://www.hanita.com/hanita_protected/climb.htm )
now they are showing a wheel type cutter, but the exact same thing applies to an endmill. One thing you should NEVER to is climb mill with a conventional ( non-cnc ) machine. This is becuase the screws have backlash in them ( that is, you tun the handle one direction & when you reverse directions it takes 1/2 turn or so befoer the table will start moving again ) Climb milling with a machine that has backlash will pull the workpiece into the cutter, breaking the cutter, scrapping the part & possabily damaging the machine. CNC machines have ballscrews which have very little to no backlash...much more rigid. Small endmills ( like under 1/4" ) can be used with caution climb milling on a conventional machine. One thing you can do is to snug up your table locks...snug, but not tight. This will help the cutter from pulling the part.

Now when dutting a slot like you are describing, yes, 1/2 the cut is always conventional & the other 1/2 is always climb. What happens here is that the cutting forces balance each-other out & you are safe.

[Gooserider]

Don't know why they can't put it in the books...

Your explanation was about what I was figuring as to the answer to my question, but wanted to be sure I wasn't missing anything...

Of course now I've found another cute issue with my POS Smithy machine - it appears the table flexes a little bit! In order to get the work up close to the millhead, I am using a couple of spacer blocks so that the workpeice is about 6-8" off the table, but still solidly mounted. Doing this, I only have to come down with the bit about an inch to make contact with the workpeice.

I was using two clamps on it, and found that even making shallow cuts and slow feeds, the setup would slip. So I added two more clamps on an angle from the other T-slot, and tightened everything up as much as I dared. My clamps are strap clamps, with the workpeice on one end, the securing bolt in the middle, and the other end held up by two 1-2-3 blocks stacked on end and a step block.

Once I had everything torqued as much as I dared, I found that the workpeice didn't slip any more, but it was also difficult to move the table. I had to really turn hard on the table handle! Once I had made my cut, and taken the peice back out, the table moved easily again. Only theory I could think of to account for it is that the cast iron table is flexing just enough to bind up the gibs. I didn't think I was THAT strong...

Gooserider