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Small parts moving11/25/16
We are new to nesting and are having some problems with small parts moving while being cut through. What can you suggest to stop this from happening. We already have 2 vacuum pumps on the machine and it is still happening.
Vac has a lot of variables, the first and probably most common fix for small parts it to cut them first, (Vac is max) and use an onion skin procedure,
all vac loss counts so check for leaks at edges of spoil board and make sure it is clean and not deep ridged from previous cuts.
I cut small parts first and use tabs as required. Very seldom have an issue with this approach.
We do use onion skinning approach but when it is making the final through cuts, that's when the parts start moving and of course the ones that move get ruined. What do you mean by tabs?
This is just a picture I found online , I don't have any of my own work using tabs . But you'll see the parts are still connected to either each other or the nested sheet with tabs. These can be like 1/8"thick and 1 1/4" long that you can just knife off after . What program are you using ?
This is the picture
Tabs are little bridges between parts or between parts and waste areas.
The picture is from Vcarve Pro. My Thermwood router does this in the nesting software also.
Question, since you are doing a onion skin ...are you cutting your parts on the first pass, leaving the onion and then going back and removing the onion skin, after you having left all your parts with a onion skin or are you cutting the part and the onion skin in the same pass.
Also are you ramping into your cut or plunging, a ramp will apply less force on the part.
Lots of factors involved here. We hold parts as small as 3x7" with onion skin (25hp regen blower) Sheets must be fairly flat. If small parts start to bow up as they are cut they can move. If you're cutting nasty sheeting this is more likely to happen.
The thinner the skin, the better. I leave a .03" skin and reduce the final cutout speed by 50%. They are cutout at 250ipm. Small parts are always cut first so they have maximum vacuum. Most software can do this.
Make sure your spoilboard is gasketed well if using a grid table. Make sure you fly cut often if cutting lots of small parts. We only cut about 15-20 sheets between fly cutting.
Also, blow off the spoilboard really well between sheets. Dust on the board acts like little ball bearings and will increase the chance for part movement.
Haven't tried this yet but how about using a 1/8 bit for the final pass after onion skinning? Less side pressure than a 3/8.
Check with your supplier and see if they have a more dense MDF, we are limited to one supplier who stocks what works for us in the size we use.
We have cabinet vision which allows us to set up onion skin parameters on all parts 4" x 6" in size. It will cut these parts first then the balance of the sheet. Running a 10hp becker with 4 x 8 table. Do check the filters because dust always finds its way into them. We also use a dense mdf and band the edges.
It all depends upon your definition of "small parts". Some items are so small there is no holding them without bridges/taps.
This past weekend I was cutting some 3/4" thick hard maple parts that were about 1" wide x 4" to 6" long. Given the shape of the parts bridges would have been difficult to clean up after removing the parts. The solution was to start with thicker material and not cut all the way through. Then I planed away most of the extra bottom thickness and finally removed the rest to free up the parts in the wide belt sander.
I cut many small parts every day using a system like onion skinning. What I do is apply 2 lines of 24" wide tape from a sign store to the back of the sheet. Then vacuum the sheet to the table down to the table. Then cut through the piece leaving the tape intact.
There are different levels of tape tack, so you can select the right option for you.
I primarily cut appleply sheet goods 1" thick with a prefinished surface.
I really like your idea of using an 1/8" bit on the final pass through the onionskin and have tried to set that up in CV but to no avail. How would you do this?
Not sure how you do it in CV but in the software that I use it's possible to to assign different cuts with different tools to the same layer of the CAD file.
The best solution I found is you onion skin or use bridges, when you remove the pieces you keep a laminate trimmer close by and flip the piece and clean it up. If you go back and try cut out the onion skin it will move on you. To use a 1/8 bit you have to do a tool change and then it still might move? Who has time for that?
How big are the parts you are trying to cut? Maybe you could post a picture? Is this a job that will be returning to your shop?