Ideas on how to hold a small part?

[gbradley]

I have a customer that sent me this part and wants to cut it out of uhmw and the size is 5.5" long X 1" wide X 1.5" thick. The part cannot be tabbed and it cannot have an onion skin due to tolerances.

Any help would be great.

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[robtown]

Double stick tape or contact cement your material to a "spoilboard" of 1/8 or 1/4 inch sintra (pvc sheet). Then screw it down and cut deep enough to cut through your material and into the sintra, but not all the way through the sintra.

[Alex Naumenko]

I've done similar parts before. I do have vacuum table. I am using .25 single flute bit .25 pass at 125 ipm. No dust collector. Last pass 0.03. Material shavings stay in the kerf and hold part in place.
Or you can make deep vacuum gasketed chuck.

[tlempicke]

If you put release tape, the kind used for vinyl sign making, on the back of the material and then spray glue it to a spoil board you will not have any cleanup to do.
Good trick I learned on this board a while back.

[RossMosh]

I know of 3 main ways to handle a project like this

1. Vacuum. If you have vacuum, you can make custom hold downs that will keep everything right in place.
2. Tape/glue. I recommend gluing/taping to a secondary spoilboard and I also recommend applying transfer tape to the back of your sheet goods. Going with a light final pass will help keep the part in place vs taking .25" on the last pass.
3. Good old hand clamp at the last minute. This is both dangerous and annoying, but it works when the run is short/small enough not to bother with options 1 & 2. I recommend running a smaller bit as it will pack the kerf which always helps. The final pass should be about .03-.05" and slow down the machine. Also be picky when it comes to your start/finish point. Picking the right start/finish point is key when using this method.

[knight_toolworks]

this is uhmw tape does not stick well and it is grabby when cutting so the bit is going to want to move it around. shavings won't keep it in place and I doubt the tape will as small as it is. of you have a vacuum bag to really get the tape to stick well it may work but I am not sure. the stuff is a bear to hold in place no matter how slow you cut it.

[scottp55]

Having VERY good luck using HDO backer board with Ace Hardware 1.88" carpet tape on waxed HDO, and then putting on 600G sanded hardwoods the No Residue Duck tape.
We wax both the HDO AND the hardwood and after wiping excess off, parts can be left on for (only my experience) 6 days before machining if weighted and a week before removing parts with zero residue and haven't lost a button from 7/8 to 1.25"D on several hundred buttons.
Imagine countertop/Corian/phenolic would be similar with testing.
Started with 3M wax and then went Beeswax dissolved in Citrus solvent for the Green people.
JUST enough adhesive on that Duck tape for a full cut through, without cutting through fabric IF FLAT.

Hope this helps George.
scott

[knight_toolworks]

I don't even trust holding larger pieces of hmw in place with just a vacuum. it is slippery and grabby enough. a 12x12 piece may still come loose without a onion skin. the shavings from this are curls of plastic that can clog my cyclone because they can stay in long pieces.

[donek]

I would guess the client doesn't really know what he wants or requires. It looks to me like the edge has been deburred with a deburing tool. A 0.020in skin is easily removed with one of these
http://www.amazon.com/SHAVIV-29249-Deburring-Handle-Pieces/dp/B003JY7LXI/ref=sr_1_1?ie=UTF8&qid=1450410903&sr=8-1&keywords=shaviv
The real question is, do you really want to do all that hand work. We make a lot of parts like this from UHMW. The hand work is what kills us every time. I have changed the design such that all the corners are chamfered slightly. We even turn them over and chamfer the back side because it is way faster than trying to run the deburring tool over it.

Looking closer, the bottom edge (near the table) appears to have been flush trim cut with something like this:
http://www.amazon.com/CMT-84201-Contractor-Laminate-Diameter/dp/B00DUQ8MLA/ref=sr_1_12?ie=UTF8&qid=1450411317&sr=8-12&keywords=laminate+trim+bit

[rb99]

Sign making transfer tape comes in different degrees of tack. If you use high tack, but first wipe off the material with 99% isopropyl alcohol it should hold. Then you can use 3M 77 spray adhesive to hold the material. Worth a shot.

Once it is cut the transfer tape comes off without any residue.

[bobmoore]

The parts in your pictures do not look like 1.5 inch thick material. You would have to run with an 1/8 bit because of the thin slot on the right side. UHMW is a bear to run with such small dimensions even with thinner material. I would say no quote if you're busy or time and material quote to verify process. Be safe with that project because I think things could get out of hand quickly.
Bob

[Burkhardt]

One more idea....
- Screw the somewhat over-size blank down on a piece of scrap plywood at the corners (double sided tape in between optional).
- Cut only the side with the arches and detail first (open vector)
- Lay a thin piece of wood on top of the still attached part and hold it down with 2 or 3 screws through the arches' openings. Large washers instead of the wood piece might work as well.
- Cut the part free along the straight back (another open vector tool path).

[gbradley]

Thanks guy's for the input. I did try cutting this part with the use of vacuum, and gasketing. I made a fixture to cut two of the parts pictured, and I will say i did cut two of the parts in the picture @ 1.5 UHMW, not the 1/2" red shown in the beginning of the thread. The process I have to cut this now is to rout out most of the material with a 1/2" up cut bit, and on one portion of this part has a .15 cut in it so i have a long reach .125 up cut bit to handle that. With the last cut I use a .25 up cut bit to rout through the rest of the material. I have never cut UMHW before so I have that learning curve to deal with. If i am going to do this job I am not going to use our big regen blower for this job I am going to use the 1/4hp rotary vane pump we have and use .03 thick, medium density gasket material to get a better edge on the part.
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[scottp55]

Pretty NICE George considering thickness/nature of material and small vac area!
Congrats:)
scott

[gbradley]

Thanks Scott!

[James M]

George,

What brand of long reach 1/8" bit did you use?

Thanks,

James

[joe]

http://www.talkshopbot.com/forum/attachment.php?attachmentid=26928&stc=1Wow, I amazed at all the options on this topic.

Here's what I do when I need little, itsy bitsy, delicate letters. After securing the substrate, route the letters deeper than they need to be. Then take the substrate over to the band saw, set the fence to the desired depth and push the piece through. To keep the letters from fall out, I use a little masking tape on the back.

There have been times when I needed several copies so I route extra deep. Then push the substrate through twice. It's so easy and fool proof.

[gbradley]

James


Sorry I forgot to answer you question about the bit.

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[bobmoore]

Sorry if I am wrong but I think this is an advertisement for vacuum fixture supplies or these are some extremely expensive little parts.
Bob

[gbradley]

No advertisement! I have never cut UHMW and it seems like I could come here and ask for an idea on different techniques on ways to cut.

[bobmoore]

Meant no offense but I would have designed your fixture to pull down to a hard stop rather than dancing on a .030 tape or use Joes idea or find someone with an old Bridgeport mill. IMO all of those options would give you faster and higher quality parts. What were your feed and speeds? How many are you supposed to make?

[gbradley]

No offense taken. I just never cut umhw and at 1.5 thick. Me, cutting cabinet parts makes this part is ridiculous size and shape to be cutting on a router. As for the vacuum fixture the foam is meant to reduce vibration to get a cleaner edge, and save vacuum to hold each part. This guy has 400 different/ similar (same but different) parts to be made 500 to 1000 at a time. I have not taken this job being as crazy as it is.

[bobmoore]

Ouch; That is the kind of project that can sink a small shop. If I designed a vac fixture for that job I would use your "in board" vacuum material and pull down to a milled corian or aluminum type base onto a strip of 120 grit sand paper to get all the traction possible for your polyethylene. Pull at least 24 inches of mercury, put extra safety glasses on and let her rip. I think you are going to get too much vibration from your "on board" material.
It would be interesting to have your guys build one of each and test run both for comparison. That would be a very informative post for us botters in my opinion.
Thanks Bob