Hold down concerns

[martmar]

Hi everyone. My name is Marty and I could sure use all the insight I can get. You see, I plan on getting the Buddy 48 for a specific project of engraving 1.25" offset letters out of a .125" sheet of ABS plastic with a 20 to 30 degree engraving bit. My goal is to cut as many as I can cut in one run. But my biggest concern is how to hold it down to cut out the pieces. The Buddy 48 is the idea machine because of its small table size and my lack of space. I like the great job Brady did on the Buddy 48 in another thread

http://www.talkshopbot.com/forum/messages/27/27659.html?1210047649

I am wondering what would be a good hold down option for this project any suggestions would be greatly appreciated.

Thanks in advance

7712

[jamesgilliam]

Marty, While never having run the type of parts you are undertaking, but having run various other small parts, I would sugggest using a spray adhesive. Personally I like the 3M Super77. I have used it with great success with holding parts as small as 1" across out of Sintra and cutting them out with no movement. Anyone else please chime in with other methods.

[Gary Campbell]

Marty...
Try setting your table up as Brady did in the post you linked to. If the ABS comes with a paper protective sheet, simply contact it to a piece of 1/4" masonite or similar. Use vacuum to hold down the masonite. A straight or downspiral bit should make sure the letters stay put.
Gary

[harryball]

I met Marty in my shop and he left me a sample of the material. I've been making test cuts using a single zone with 2 feins. I cut a small badge about 1.25" x 5" successfully with a 30 degree bit. For Marty's application I think holddown is the challenge. One advantage he has is that his project will be using a vbit to cut all the way though, this means the kerfs will be relatively small from the vacs point of view.

The material cuts like butter. My approach was to cut 90% through the material then come back and make a final pass to cut it free. It worked but left more tooling marks than will be allowed in final production. The material also "snaps" well when scored. For my next test I'm going to leave the long edge with a slight skin and see how it snaps out.

Spray adhesive and using a 1/4" masonite base are also interesting ideas. Perhaps repositional spray adhesive combined with a masonite backing/spoil board might do the trick. I'd also considered making a vac mask out of "self healing rubber".

I'm sure there are hundreds of ways to do it, just have to experiment to find the best combination.

/RB

[harryball]

Another thought... I suggested working with 2' x 2' blanks sort of as the standard to help with the vac solution as well as storage and being able to upgrade production. These badges are going to take 1 to 2 minutes to cut with the detail. My idea is that a second Z could be installed on the Buddy 48 yoked at 0,24 and he could cut 2 blanks at one time doubling production in the same amount of time. Is the Buddy going to be capable of that upgrade?

/RB

[dana_swift]

I with James on the Super 77. I use it to hold small parts to HDPE which is then held by vacuum. That lets me cut all manner of small parts with no shift at all.

Marty- my best advise is you can trust that a shopbot can do the job. If your really want large production and cut as many parts as possible, look into a gantry system and work with large sheets of material. I use a BT-32 for all kinds of stuff, and for extra long projects I bought an 8' powerstick. I don't intend to use the powerstick for routine use tho.. i work mostly with the "normal" table.

Talk to the sales people at Shopbot, tell them what your intentions are and what your budget is. I'm sure they can help make an appropriate choice.

Good luck- and looking forward to hearing how your parts are coming out!

D

[knight_toolworks]

I have been cutting thin plastic. it has a problem of lifting up. so a vacuum can be a pain unless it is really strong.
I am doing a 4x4 sheet right now with 2"x25" pieces with 50 holes in each piece. the spray adhesive has worked well so far and has not added much time. less then it would take to score the pcies and such.

[martmar]

Thanks to everybody who has posted thus far. I understand the spray adhesive option. But my biggest concern with that is clean up. I really cant have the plastic contaminated. My plastic does not come with a paper protective sheet so I would have to spray directly onto the plastic. Is there a sure way of cleaning them off? If so then that may be a good option.

As far as a vacuum setup for this project to work, what kind of vacuum power would it take? Would a Fein or two work for a specific area or does is take a bigger vacuum source?

[knight_toolworks]

no backing is not as nice. but paint thinner cleans it well and will not hurt the plastic.

[martmar]

Hmmmm I might have to opt out for a gantry system if the adhesive spray will do the trick. But I would really need to research that because I am going to be painting the pieces next. What affect would paint thinner have on the plastic when painting?

[carlcnc]

Marty
I use 24" wide application/transfer
like is used for vinyl signs.
get the high tack[60$ per roll]
stick this to your material then glue to a sacrifical board.masonite works well,
you can just peel your pieces from the tape and you're done.
Carl

[harryball]

Again, it sounds like working with 24" x 24" blanks would be a good approach. I have some 15" wide transfer tape and I believe some 77 adhesive as well as some masonite scraps. I'll have to give this a shot and see how it works. I'm a bit busy the rest of the week, it may be Saturday before I get some free time again to play.

Any my second Z should be delivered today! wooohooo!

/RB

[joe]

Fellows,

Would some neatly positioned 3D bridges be completely out of the consideration?

At my little shop we cut .50 and .75 thick Extira letters with 24, 30, 45 degree V bits on a regular basis. The neat thing about V bits, when making multiplal passes, is they automatically clean up the precious cut. I make a couple of passes on Extira because it keeps the sould level down and smoooths of the letter sidewalls. I usually run at 2ips and 14000. This may seem slow but the advantage is very little clean-up.

These are special bits and aren't cheap. So I baby them. I've previously posted pix of these. I think Gary Beckwith is now having them custom built. www.beckwithdecor.com (http://www.beckwithdecor.com) and available to the public. For a couple of years I paid big bucks to have them custom built and that took a long time.

You need a good vacuum pick-up with this material. The dust is heavy. Good thing though, it's not as prone to be airborn as other fiber board substrates.

I leave a nice, fat, couple of bridges on each letter. Sometimes three bridges on skinny letters like the "W" or "Y"'s. Those are .30 in depth and .45 in legnth. Once the panel is finsished I drag the whole sheet over to a table and pop the tabs off with a sharp chisel. Then it's a quick buz on the 1" table top sander with the table set at the proper angle. That goes fast.

I don't do high production, however Terry and I made about two hundred of these in the last two days using FAT tabs. We'll get this kind of order once a week. The reason being we're the only CNC shop in the area with those big 2" depth V bits.

Some of these letters were 4" but the largest were 18" & 21". Makes no difference as to stability with large tabs.

I like useing the word Fat. My appology.

Joe
www.normasignco.com (http://www.normasignco.com)

[dana_swift]

Marty- there is a simple experiment you can do to see if my method of getting the adhesive off the parts will work for you.

Get a small piece of your material, spray super 77 on it. Stick it to a test block of HDPE, plywood, or whatever you intend to use. It only takes contact for this stuff to setup, I let it sit for a minute or two before I start cutting on it to be sure its solid.

Wait about 10 minutes while the "router" would be doing its job. Then separate the parts from the substrate with a knife.

Now dip a reasonably clean rag in naphtha, wipe the residue off your parts.

Check your parts for damage from the naphtha. Most plastics dont mind nahtha because it is such a weak solvent, but plenty good to get rid of the supper 77 goo.

No scrubbing required, it just wipes off with the first light pass!


Let me know how it goes!

D

[GlenP]

Marty, I have cut 2" letters in pvc and used two sided tape to hold them down. I bought the tape with the mesh in it and it just pulls off when done. I used coroplast under the pvc and cut right through the pvc and into the coroplast. I two sided tape the pvc to the coroplast and then screwed the corners of the sheets to the table. I works great. I found using a wood material for the spoilboard sheet left a residue on the pvc.