[cordvision]

I often have to face large stock pieces that don't fit into my vice. I was wondering what method/tools you like to use to fixture large stock for facing? I would prefer being able to face the entire top surface without having to re-clamp. Also, can't put holes in the stock to screw it down.
A vacuum table would obviously be ideal for this, but i'm sure there are other alternatives.


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[hanermo]

Metal ? Plastic ? Wood ?
Size ?
Goals ?

One good, cheap, solution is to drill bolt it on the edges, and then machine the edges off.
More detais will get you better answers.

Ice chuck if its small, steel.
Against edge-mounted gage pins is one option, for moevent/alignment.

2-part vices is another.
These are 2 different pieces, and can clamp a say 1x2 m piece of flat steel.

[CadRhino]

I am in the process of figuring this out right now too. In my case o have a 14" diameter plate I need to face and machine. I have a tormach 18"x18" x 10mm aluminum palate fixture but since this part needs to be nuts-on precise, I am planning on mounting it to my 4th axis in the horizontal position. I will use the superfly to face the part by moving the 4th axis.
If you don't have a 4th, I think you need some kind of fixture plate you can flip with reference holes or pins to reference your part.
Good luck.

I often have to face large stock pieces that don't fit into my vice. I was wondering what method/tools you like to use to fixture large stock for facing? I would prefer being able to face the entire top surface without having to re-clamp. Also, can't put holes in the stock to screw it down.
A vacuum table would obviously be ideal for this, but i'm sure there are other alternatives.


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[Hirudin]

Is clamping the part between jaws attached to the outside of the vise a possibility?

(like this: http://www.frets.com/HomeShopTech/To...kurtjaws02.jpg )

[GLCarlson]

I often have to face large stock pieces that don't fit into my vice. I was wondering what method/tools you like to use to fixture large stock for facing? I would prefer being able to face the entire top surface without having to re-clamp. Also, can't put holes in the stock to screw it down.
A vacuum table would obviously be ideal for this, but i'm sure there are other alternatives.


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Mitee-bites! Either the cam operated hex t-nut holders or the hardened Versagrip or Talongrip. Might have to use a subplate to get the fixturing right. 14" diameter might be a bit big.

Vac table might work, but they're harder to build than they look at first glance.

[Steve Seebold]

I am in the process of figuring this out right now too. In my case o have a 14" diameter plate I need to face and machine. I have a tormach 18"x18" x 10mm aluminum palate fixture but since this part needs to be nuts-on precise, I am planning on mounting it to my 4th axis in the horizontal position. I will use the superfly to face the part by moving the 4th axis.
If you don't have a 4th, I think you need some kind of fixture plate you can flip with reference holes or pins to reference your part.
Good luck.

If you do it on your 4th axis, I would just use double back tape to hold it down and if your finished part is round you can do that at the same time.

[CadRhino]

Good idea Steve
I might use tape for the facing operations and getting a few fastener hold-downs. After that, the piece will soon be cut up into Swiss cheese.

If you do it on your 4th axis, I would just use double back tape to hold it down and if your finished part is round you can do that at the same time.

[CadRhino]

Steve,
I just ordered some Permacel double sided tape.
One question for you is how to release my part from the fixture plate.
Here is the scenario - I have a 1" thick by 9" Diameter aluminum fixture plate bolted to the face of my 8" rotary table (using the T-slots/bolts on the face of the RT).
I will have the 1/4" thick x 14" aluminum plate taped to the top of this 9" fixture plate.
After fly cutting the top, I want to flip it over to fly cut and machine the other side.
I have read that denatured alcohol is used to break the bond of the tape.
Since my fixture plate is smaller than the plate I am machining and it is bolted to the face of the rotary table, my challenge is how do I get under the machined plate to 'break' the bond of the tape between the part plate which overhangs the rotary fixture plate by 2 1/2" on each side.
I think typically fixture plates are larger than the parts but I would have to take out a second mortgage to buy a big enough fixture plate and I already had the 1" x 9" diameter round stock.
I could tilt my RT but it is heavy and I will have to re-align it.

Thanks,
Nathan

If you do it on your 4th axis, I would just use double back tape to hold it down and if your finished part is round you can do that at the same time.

[cordvision]

Thanks for all the replies. I'm mostly machining aluminum (some of it with the hardness off mild steel 7075). I was thinking using mitee-bites as well. BTW, is there nothing like mitee-bites that go on top of T-nuts, so you don't need a fixture plate? You could slide them in the t-slots until they are snug against the stock. This would essentially turn your whole table into one large vice

[cordvision]

Hmmm, going to try that with my Tormach machinist vice. Need between 8-10" of clamping. Only problem is that the stock will sit very high in the vice.

[mountaindew]

Steve,
I just ordered some Permacel double sided tape.
One question for you is how to release my part from the fixture plate.
Nathan

My notes on double sided tapes
Clean both surfaces with alcohol or the tape wont stick very well.
Figure out some crafty way to press / clamp it down or together to help tape form bond. Leaving it clamped for a few minutes also helps.
Machine it dry or part will fly

I use a long narrow blade putty knife to break tape bond and release parts.

The tape has thickness and the thickness can vary, causing problems.
The tape also has flex or spring this also causes problems to consider.
md

[CadRhino]

Thanks md
What brand tape are you using?
The brand I will be using is pretty strong adhesion but the prying might work to break the bond if I am careful not to gouge the part. The part will be pretty delicate when I am done so I was looking into getting alcohol to the tape to help break/dissolve the bond
I guess I just need to try it and see how it works

My notes on double sided tapes
Clean both surfaces with alcohol or the tape wont stick very well.
Figure out some crafty way to press / clamp it down or together to help tape form bond. Leaving it clamped for a few minutes also helps.
Machine it dry or part will fly

I use a long narrow blade putty knife to break tape bond and release parts.

The tape has thickness and the thickness can vary, causing problems.
The tape also has flex or spring this also causes problems to consider.
md

[CadRhino]

That would be a good invention. I bet you could rig up aluminum bars bolted down to the t-slots with cam locks on the top.
Are you making another big injection mold?

Thanks for all the replies. I'm mostly machining aluminum (some of it with the hardness off mild steel 7075). I was thinking using mitee-bites as well. BTW, is there nothing like mitee-bites that go on top of T-nuts, so you don't need a fixture plate? You could slide them in the t-slots until they are snug against the stock. This would essentially turn your whole table into one large vice

[mountaindew]

Thanks md
What brand tape are you using?
The brand I will be using is pretty strong adhesion but the prying might work to break the bond if I am careful not to gouge the part. The part will be pretty delicate when I am done so I was looking into getting alcohol to the tape to help break/dissolve the bond
I guess I just need to try it and see how it works

I mostly use pattern makers tape "paper type" from Double Faced Adhesive Tape - clear VHB and white foam
This is specific for use with plastics and might not work for your application. "stuff is not cheap either"
If the part is delicate it would be good idea to use some sort of bond breaker like alcohol.
Low force operations will also help the material stay in place until its finished

ps: post some pics of your finished part or work, always enjoy looking

[wildwhl]

Steve,
I just ordered some Permacel double sided tape.
One question for you is how to release my part from the fixture plate.
Here is the scenario - I have a 1" thick by 9" Diameter aluminum fixture plate bolted to the face of my 8" rotary table (using the T-slots/bolts on the face of the RT).
I will have the 1/4" thick x 14" aluminum plate taped to the top of this 9" fixture plate.
After fly cutting the top, I want to flip it over to fly cut and machine the other side.
I have read that denatured alcohol is used to break the bond of the tape.
Since my fixture plate is smaller than the plate I am machining and it is bolted to the face of the rotary table, my challenge is how do I get under the machined plate to 'break' the bond of the tape between the part plate which overhangs the rotary fixture plate by 2 1/2" on each side.
I think typically fixture plates are larger than the parts but I would have to take out a second mortgage to buy a big enough fixture plate and I already had the 1" x 9" diameter round stock.
I could tilt my RT but it is heavy and I will have to re-align it.

Thanks,
Nathan

Couple of thoughts on releasing Nathan -

You could use a little heat to soften the bond (heat gun).

Also, might have already been suggested, but waxed dental floss may allow you to saw along and break the bond. Might take a bit, but would eliminate any tweaking/bending of the plate caused by trying to pry it free.

Bill

[MichaelHenry]

I've been using this 3M tape and have had good luck with it, even with flood coolant, so long as I'm quick and there isn't a lot of through penetration or peripheral milling. It should work just fine for surfacing only. I get it from McMaster-Carr, but can't find a part number in their web site. They should be able to cross-reference it if you call, though. I've used ethanol or acetone and a bit of prying to free the part from the fixture plate. If you try this, it might also be a good idea to to put a rail along the edge that the cutter will be movng toward, especially if you expect to be taking aggressive cuts or using a large diameter face mill or fly cutter.

The T-slot Kits from Mitee-Bite are also a possibility if your stock is high enough to clear the T-slot clamps.

Mitee-Bite Products Co.

and

http://www.miteebite.com/images/prod...slot_kit_2.jpg

but on large footprint stock you make have issues with chatter near the center of the work. A bit of double-sided tape in the center might help there.

Another possibility is hot glue adhesive, applied along the outer edge of the stock where it meets the fixture plate. I used something like that to mill a large piece of piece of aluminum (from 1-1/2-in thick to 3/16-in thick in places) where I was concerned about chatter. It worked better than I'd hoped and the adhesive just peeled off at the end of the job.

Attachment 274716Attachment 274718

[LeeWay]

The 3M double sided tape I have is called VHB tape. (Very High Bond.) That stuff is not letting go unless you need it to and then not without some effort.

MC part number #76665A81. Be prepared for sticker shock. Pun intended.

[ger21]

You can get VHB tape on Ebay for a fraction of it's retail price. It is a thick foam tape, though, so not the most rigid bond. But it does stick like crazy.

[LeeWay]

The stuff I have is clear. I have used it a bit for R&D. Works great in that capacity. Foam would probably do just as well.

[CadRhino]

The stuff I bought is made by Nitto/Permacel. I have seen it used by a number of machinist and turners so it sounds good.
VHB tape is way to strong. I use it for external applications profile solutions. That stuff is really amazing.