can you screw down and cut several sheets of plastic at a time?

[knight_toolworks]

I was trying to cut some lexan that is .09 thick. that parts are not large the smallest is about a 5"x3" triangle with two small holes.
but the problem was I was getting rough edges.
I found it was the pieces vibrating while cutting. my two fiens were not cutting it. I was using a 1/8" straight 2f bit at 1ips. I could sometimes cut smooth at .75 but it was a crapshoot if they would cut cleanly or not.
the sample he showed me for another cnc place it was really smooth and either they had a high end cnc or they screwed them down.
I thought about making a brady vac for a sheet but time wise it would make it so I could not make enough on the job.
but if I could say cut the sheet in 4 peices use thevac to hold them and drill all the holes the stack and screw them to the holes in the table I could the whole sheet in a pass or two. it would not be practical to screw a hole sheet down as it would be 500 screws.
so reducing that by 3/4 and cutting the whole sheet in about 1/4 the time would make it cost effective.

[ken_rychlik]

The faster you cut, the smoother your cuts will be. I have used two sided tape along with my feins and it works pretty good.

A down spiral zero flute will help with the lifting.

The plastic with the paper backing will stay put on the vac table MUCH better than the plastic protective film.

You can stack sheets with two sided tape and it works fine. You just have to pay for the tape and time to deal with it.

The only problem when stacking sheets is when you screw up, you screw up a lot of sheets. lol

Kenneth

[knight_toolworks]

can't use a downcut because it's plastic and it makes the burr stick. I really miss downcut bits on plastic. it just would not be practial to stick down sheets. for this job. I mean 4x8 sheets are a little hard to stick down (G) then the time to remove them. the protective sheet would need to be removed before I cut as I don't like the idea of removing 1000's of pieces from the parts afterwords.
I debated on making a small vac table that would use the brady method of holes under each piece. but I am not gettign paid for doing any of that so I don't want to spend the time.
screwing 4 1/4" sheets down at once would be ok better 125 screws verses 500 and it would make cutting time practical. but I don't know if it would keep the parts vibration free.

[ken_rychlik]

Steve, I am using downcut zero flutes on plastic.

I got em from Gary Beckworth.

You have to move fast so it won't remelt.

Kenneth

[Brady Watson]

For production, Screws = Bad News. The holes get all wallard out and you'll lose holding power. Not only that, but screws distort the material, causing other unforseen problems.

I get agita any time someone mentions stacking sheets...It's something that customers a la el cheapo try to get me to do before I have to educate them on the false economy of doing this...Like customers who want to common kerf cut 1" MDF with an 1/8" bit. It's all ree-donk-u-lous for those of us that know what is the right way to cut parts.

I've been involved with several time consuming & stressful projects lately, and really didn't want to roll this idea out to the masses until I had the time to do a proper write up & get it into my 'in much need of an update' web column on the SB site....So, that being said, I'll do the best I can to get the idea across, if for nothing other than to ease the pain I sense you are feeling right now...

Go Read This Right Now (http://www.talkshopbot.com/forum/showthread.php?p=99461#post99461)

-B

[jerry_stanek]

Does each sheet have the same parts? If so make a dedicated vacuum jig to hold the parts and any small areas that need to be held down.

[knight_toolworks]

accuracy is not a huge issue since these are simple parts for a fishing lure. but a smooth edge is. a 16hp vac is the way to go.
Now another question I may get a call for a quote to drill 1/4" plywood. they want it for a ceiling panel. I am thinking if vacing one sheet stack a couple more on and drilling at the same time. since these are only getting drilled I can't see a problem. sound ok?

[Brady Watson]

Steve,
Did you check out the link I posted for you?

-B

[knight_toolworks]

Steve,
Did you check out the link I posted for you?

-B
yes it was great info. I like it better then using contact cement.
I agree screws are hard to make money on. the only way would be multiple sheets. for once I gave up on the job.
but do you think it would be ok for drilling holes in plywood? it is just for ceiling panels. a brad in each courner would be enough.

[Brady Watson]

...but do you think it would be ok for drilling holes in plywood? it is just for ceiling panels. a brad in each courner would be enough.

That's hard to say...I think the only way I would do this is with a 2 flute straight that is center cutting. Spiral tools will cause the sheets to walk up it & jamb swarf between the sheets - exacerbating the issue. A downcut is a no-no too, because it will jamb the chips under the last sheet & possibly the middle too.

If you keep the safeZ height low, and run at 2 IPS on the Z, I see no reason why you couldn't go one hole per second. I've done this many times on my machine and timed it. 1200 holes in 3/16 acrylic in 20 minutes.

How many holes do you have to cut into a 4X8?

-B

[knight_toolworks]

I was thinking the same thing about lifting. maybe peck drilling the depth of each sheet. if they want 3/4" on center about 8000 holes per sheet.