acrylic joint fitup?

[metarinka]

hey I currently have a modding project for my sophmore fabrication project at uni. Needless to say while it rocks to get a grade for modding and have access to a full fabrication and machine shop I need perfection and it's an ambitious project. to make a long story short I have an 1/8" acrylic sphere and I need to cut some holes in it. First of all I'm just guessing preventing this giant (24") globe from cracking is going to be a pain, and that I'll have to make a wood die on the insides to take the weight of the drill and prevent deformation and maybe help with squaring.
now here's my questions I need to make some clean joints. the problem is I'm trying to mount http://www.usplastic.com/catalog/pr...duct%5Fid=11248 clear acrylic tube to a sphere so just joint fitup and squaring is going to be strange, the real problem is does any one know the tolerance of hole saws? and acrylic tube? I was thinking of using 4.5" acrylic tube and a 4.5" hole saw but I'm not sure of dimension tolerance as I believe acrylic needs a flush joint? I suppose I could cut say 1/2" too small and ream it out with a die grinder, but as you all know trying to get an exacting cut in plexi with hand tools isn't easy.
also can anyone reccommend cements or glues for acrylic? this tube wouldn't be under any other force save for its own weight. I also have access to a plastic welder but hot gas plastic welding tends to deform vaccum formed acrylic.
Any general guidelines to cutting holes in acrylic (especially formed spheres)
That sphere is $150 so I don't want to fudge it on the hole cutting, drilling, or bonding.

[billbartuska]

[quote=metarinka]hey I currently have a modding project for my sophmore fabrication project at uni.... I have an 1/8" acrylic sphere and I need to cut some holes in it. /QUOTE]See http://ozreef.org/content/view/66/29/

Your linkey didn't work so I can't see what you want to glue on.

How about glueing in a short piece, 1/2" or so, of whatever it is with just two small dabs of glue (clear, thin type) over a predrilled hole that is smaller than the part glued on. Then use a dremel, with the part as a guide, to open up the hole? Then break off the temporary part and permenantly glue on the real part. Perhaps some practice gluing and breaking will help getting the temporary atrtachment to where you need it. And be carefull using a dremmel to polish acrylic..they can be way too fast, but work, if used with care. Again, practice.

[bigben2k]

Weld-On #4
It'll make a chemical bond between acrylic pieces.

[blue68f100]

Hole saw are nominal, and will have a runout approx .0625 or greater, depending on how tight the mount is. They do not give a clean cuts, like other do. The most precision way would be with an endmill. I would proably use a fly-cuter. Some fly-cutters hold endmill cutters, instead of the standard insert. These will give you more control. Stay-away from carbides cutters, they require greater interface/force to cut. This is going to be a difficult cut, take your time. As for a cutting fluid, you will have to look and see what's on the market now.

[metarinka]

thanks for all your help

oops link got truncated http://www.usplastic.com/catalog/pro...oduct_id=11248

4/5" acrylic tube with a 1/8" wall. Thanks for that infor blue that is helpful. Will a fly cutter work on a sphere though? I thought about that, and I'm sure my shop has one but don't fly cutters have to be perpendicular to the surface.

that sounds like an interesting strategy as well billbartuska. In total I believe I'll be cutting 4-6 holes in 3 sizes, the smaller sizes will be tangent to the surface so this seems like a good way to mark up those holes. I'm dense as the tube only needs to be mounted to the "inside" of the sphere so hole diameter shoudln't be as exacting. I.e I'll be mounting a tube over a hole, not trying to fit it IN the whole and flush to the surface.

any clue as to the where to purchase weld-on acrylic glues?

[bigben2k]

Google for it, there's a US outfit that you can call.

[metarinka]

yah found it about .02 seconds later on google

[Marci]

Some of the info in this thread may be useful...

Tensol 70 Cement (by Bostik Findley.. also available from Amari at a luverly price of £17 for the 2 part pack). This comes in two parts, which should apparently be mixed at a 20:1 ratio. At this ratio, it dried instantly. Good job some testers were done before attacking the main panels... also the added advantage of having an excessively large sheet of perspex is you can make some little tester offcuts so you don't knack up your main panels. A bit of experimentation and the perfect mix was obtained to give suitable "manouvering time" to get the panels in place and together before it set, but not too long cos we didn't want to be stood round all day waiting for it to dry before we were safe to let go.