cutting out small parts

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cutting out small parts

Postby redwood » Wed Oct 03, 2018 12:04 am

I have some toy vehicle designs from MakeCNC that I'm hoping to make for a charity to give away at XMAS. I'm cutting them out of 1/4" Baltic birch plywood. I'm wondering if I need tabs for these little parts. I've actually cut out 2 vehicles already. I had setup tabs, but they didn't hold or I cut through them. None of the parts seemed the worse for wear, despite being completely cut out and a couple popped out of their places.
I'm using a 1/16" downcut endmill. To give you a idea of size, the preview is a 2' x 2' square and the assembled vehicle is around 5" long.

My question is? Was I lucky that nothing went flying or was destroyed. Or is safe to just cut them out without tabs.

farmtruck.jpg

farmtruck.jpg
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Re: cutting out small parts

Postby garylmast » Wed Oct 03, 2018 12:08 am

I would use tabs. If you are using a dust collector, it will also save from sucking up the small part.

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Re: cutting out small parts

Postby redwood » Wed Oct 03, 2018 12:30 am

I normally use a dust collector, but I wouldn't for this. Not using tabs would be a huge time saver in not having to cut them all out, as well as not having to place the tabs. There are approx. 33 pieces in that car.

With 1/16" endmill, I'm taking 5 passes to cut them out. I have no idea what happened to the original tabs in my first try. They were setup as .1" thick x .375" wide.
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Re: cutting out small parts

Postby highpockets » Wed Oct 03, 2018 12:58 am

How are you holding the plywood down?

I'd use painters tape and ca glue. Make sure to have the tape covering at least a portion of each part. https://www.youtube.com/watch?v=r6DCvtcU8_M
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Re: cutting out small parts

Postby Adrian » Wed Oct 03, 2018 10:57 am

Where are you setting the z zero and how accurate is the thickness of the material?
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Re: cutting out small parts

Postby 4DThinker » Wed Oct 03, 2018 12:17 pm

Your tabs likely disappeared because the depth of cut was a bit more than the actual plywood thickness. Rarely is 1/4" bb plywood actually 1/4" thick. When I do small part like this I'll pocket away small inner waste areas so I don't have to worry about making/dealing with tabs for those. I'll leave out tabs on large pieces if I'm watching the CNC as they cut and can usually reach in and hold the piece in place on the last pass. Otherwise I measure the true thickness of any material I'm using with a digital caliper. Set that in Vcarve. I make tiny tabs for tiny pieces usually .05" by 1/4" long, trying to only do them parallel with the grain on the bottom layer of the plywood. 1/4" BB plywood is often 6mm or .236" thick.

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Re: cutting out small parts

Postby redwood » Wed Oct 03, 2018 6:37 pm

I did measure the plywood with calipers, it was .196". I held down the 2'x2' ply with 8 holdowns. There was a very, very slight bow of the plywood in the center, which I didn't realize until the parts were cut out and I could see the ever slight movement when I pushed down on the plywood.

I actually ran the profile toolpath at .196", with the tabs. The tabs were present, but it didn't appear to cut all the way through the ply. I released one side of the holdowns and lifted the ply and confirmed it did not cut all the way through. So I added .005" to my cut and all but 2 pieces cut all the way through, but also eliminated my tabs. That may have been the result of starting my profile cut at .196" and cutting .005" deeper.

My point is that everything turned out fine and saved me a ton of time cutting all those tabs. I'm hoping to make 16 of these little vehicles, so we are looking at approx. 500+ parts. My hope is/was, that using such a small endmill on very tiny parts allowed me to get away without any tabs. Not one piece was damaged. Was I just extremely lucky?
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Re: cutting out small parts

Postby Adrian » Wed Oct 03, 2018 9:07 pm

All depends on the material, bit type, cut direction and finishing point. Many items I cut I don't use tabs or any method to hold down the cut part and it works fine with large and small pieces. Same thing in a plastic rather than wood or with a different cut direction or finishing point and it's flying halfway across the room before it's finished.
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Re: cutting out small parts

Postby scottp55 » Wed Oct 03, 2018 11:34 pm

I'd recommend John's method, but never personally used it (but just bought materials to try it).
After trial and error we came up with a method remarkably Like Russ's;
https://forum.vectric.com/viewtopic.php?f=27&t=26319&start=30 (end of page 2- beginning page 3)

BUT didn't have any vinyl transfer tape, so used Duck brand "No Residue Duct Tape" and Ace Hardware 1.88" double sided carpet tape in pic because on the other sizes the paper sticks awful.
Used this method on waxed HDO for thousands of buttons and keyfobs down to 1"D and cutting out with Drillman1's .25" 60 degree vbit and whiteside .5" .25"Radius point cutting roundover which has a LOT more force than yours.
Most were .2" thick.

Closest thing to your project I've personally done with no problems was some "Twig" butterfly joint inlays(.22" thick) for an Ebony piece that developed a crack on Mom's XMas present...so I just used the same set up as buttons, and it worked a charm. Pics look like it's not a clean cut, but I cut a little deep and that was sawdust mixed with carpet tape residue and came of with rubbing my finger across it.

Been thinking of trying CA between two pieces of the No Residue Duck Tape, but haven't needed it yet.
IF I had tried masking tape/CA personally......?

IF! Your material were totally flat on the spoilboard, then I might try just letting the Downcut pack the kerf with sawdust and hold it in place like a fair amount of people do after experimenting. AND if going .005" deeper than material for the cut out, I'd make the last pass .01" to leave just a skin to be cut on the last pass.
That takes a perfectly flat spoilboard, and I'd reference to the spoilboard.

Just thought I'd mention it.
scott

Oh, Maybe nest a lot closer together, and possibly group the individual types of parts for all the trucks together for tighter nesting and less sheets?
I hate screws, but they're better than having the sheet bowing. After nesting and toolpathing, make a circle larger than diameter of screw head, and with actual cut showing in blue in 2D view, place circles in areas that are safe.
Attachments
CHAD 5.jpg
DRILLMAN 1 .0625 DOWN MOM MALE INLAY 2.jpg
6.5.17 SASSAFRASS MOM'S TWIG SMALL.jpg
6.5.17 SASSAFRASS MOM'S TWIG SMALL RELEASED.jpg
DRILLMAN 1 .0625 DOWN MOM MALE INLAY.jpg
Bloodwood Bonnies cut 11.11.15.jpg
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Re: cutting out small parts

Postby scottp55 » Thu Oct 04, 2018 12:06 am

Dug for the uncropped pic of actual tapes that worked best.
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Re: cutting out small parts

Postby ger21 » Thu Oct 04, 2018 2:39 am

A 1/16" bit will have very low cutting forces, so plain old double faced tape would be the easiest method. My preference is golf club grip tape, which is similar to plain old tan masking tape, but two sided. It's very sticky, but easy to get off. Much, much better than carpet tape imo.

And your .196 BB is 5mm.
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Re: cutting out small parts

Postby scottp55 » Thu Oct 04, 2018 3:01 am

I agree with Gerry, that using carpet tape by itself is a sticky, time consuming mess...but used like Russ and I do as a sandwich between two layers of no residue tape like his vinyl transfer tape, or my Non-Residue tape is great:)
Gives just enough thickness so if something is off a bit, you don't cut into your carrier board.
The tack on that Duck tape is probably more than you need(about 2/3 of regular Duck Tape and 50% of Gorilla duct tape), but releases extremely clean even after the stated "90 days".
Cut some Bloodwood for John from a scrap that had been on the HDO for a year and released clean:).
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Re: cutting out small parts

Postby SteveNelson46 » Thu Oct 04, 2018 3:04 am

Turners tape works pretty good too. Woodcraft has a couple of different strengths. Also there's the double sided tape that has the red pull tape and labeled as "permanent" (Home Depot). Nothing is permanent but that stuff really sticks.
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Re: cutting out small parts

Postby kstrauss » Thu Oct 04, 2018 9:12 pm

I use https://www.amazon.com/gp/product/B000QDL9GK/ when cutting tiny parts from thin plastics such as Delrin. It isn't cheap but is much thinner than most carpet tape and is cleanly removable.
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Re: cutting out small parts

Postby KeithW » Sun Oct 07, 2018 6:48 am

I use green masking tape (2" if project allows) and CA glue. It is worth trying!

Clean spoil board, (no dust etc), put tape down and rub it down

Clean back of board, put on tape and rub it down well also.

Run a small bead of CA glue on the tape on the spoil board, and spray the back of the other piece with accelerator, and then put it down on the other tape.

Be careful not to get any glue on the spoil board OR YOU WILL be stuck down!

It doesn't take every much to hold. When finished just pry it up; it's only like masking tape coming off of a board.

Beats any other hod down, especially for cutting of small parts.
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