We’re running a Biesse Skill with two Busch MM 1322 AV vac pumps and generating our nests with CV. I have True-Shape-Nesting and pack my parts fairly tightly. We make booth seating for restaurants so the parts are smaller than a typical cabinet job, with that, I feel like I have to keep the feed rate lower to keep the parts from flying off the table (we still generally chew up 2 parts per 10 nests. We do use an onion skin but trim that on a final pass for the smaller parts. Our go-to bit for cutting most of our ¾ panels is the Onsrud 60-173MW which is a ½” two-flute spiral compression with about 1/8” up-shear. We run the bit @ 410 IPM and 10,000 RMP. It usually takes about 13 minutes to cut one nest and we obviously would like to cut that down.
My question to all you folks is; what tool are you using to cut ¾ ply, and what is your speed and feed? Any thoughts on how I can improve my time?
I've attached a typical nest diagram for your review.
When cutting diewall parts, which are not too dissimilar from what you are describing I onion skin at 720 with a Vortex 3130XP, which has about 1/2 inch of up shear, mostly for chip evacuation and edge quality. I have plenty of vacuum, but no amount of vacuum is going to get 100 percent of veneer core plywood parts cut without screwing a few of them to the table.
I don't know if you can do it in CV, but in AlphaCam I can pretty quickly adjust the starting and stopping points of each perimeter path then order the tool paths to leave the largest part cut last. This way each part in a nest is still attached to the main body of until the cut is just about complete. If there are no large parts or if I need to end with a smaller one I place a couple of 5mm holes in the last part or two in a nest to be cut and screw them down to the spoil board. If a part is very small it gets a screw in it as well.
If you do a ton of this stuff Thermwood has a machine with a hold down roller for just this kind of thing.
I got so sick of losing parts or banana parts for the speed we are running I started to run return onion skin on all parts and leave 2" parameter on the edges for a better vac. Since we can run a fly cut on every nest, I just started doing that. Its cheaper that cutting trashed parts on the saw or recutting
I am curious what kind of spoil board material you are using. I only ask because I know that when were first getting started with our cnc, we tried using MDF for the spoil board instead of LDF (or MDFUL). There was no compairison. The LDF allows a lot more air flow and gives much better hold down.
With a nest like the one you are showing, you are going to be bleeding a lot of vacuum by the time it nears completion. You might try increasing the skin thickness to help keep the vacuum from escaping and keeping your spoil board surfaced regularly so you are not loosing so much around the edges.
We use the same Onsrud cutter as our main plywood cutting tool and typically run 800ipm with 18,000rpm. We don't run a lot of small part nests like you are running but we do have small toe kicks and stretchers in our nests and don't have issues with them moving as long as they are onion skinned.
I would use a 3/8 bit. We use a Vortex 3184XP on plywood.
We cut parts that are too small to cut on a CNC. Those parts always come with larger parts and we leave a skin between those parts. We have a flush trim router on the outfeed table of the cnc to zip them apart. Never fails.
You appear to have many similar small/thin parts. Can you join multiples and trim them apart after?
We do use standard MDF because we felt the LDF had too much vacuum leak. The problem we face is that we use a pusher off feed on a 5x12 bed, with that, putting cover sheets over the spoil board became tedious and we opted to slow down the bit while using regular mdf. We do have gasketed zoning and what happens with the LDF is that the vacuum leaks through the edges.
We do use onion skins for small parts but the problem with CV is that it doesn’t give me the option to leave the skin, it will always cut the skin off, risking the smaller parts at higher speeds. I’m going to experiment with tabs but the same problem exists.
We mostly do pod hold down on our CNC so don't do much spoil board work. As such we have 4 separate spoil board units (a Shopbot forum idea) that we mount to the MDF screw down table surface when we want to cut sheet stock. Four units at 24 x 48 each give us a 4x8 through vacuum fixturing surface.
When cutting parts smaller than the throw-on thru vacuum fixtures we use cardboard scraps to cover the open space. We have a lot around because we make our own boxes to ship our mouldings. It takes just seconds to cut a scrap to size to cover an open section of spoil board.
By using the MDF you might not have as much loss on the edges, but you are also not getting enough vacuum where you need it, under the parts. By using MDF, you are not just sealing the open areas, you are also sealing the work area and drastically reducing your hold down power.
When we get our spoil board sheets, the first thing we do is paint all the edges to seal them (we use whatever latex paint we happen to have). We have a 5x12 table but typically only cut 4x8 sheets so we have gasketed off below the spoil board where it is not used. When cutting smaller parts than 4x8, we use pieces of 1/4" plywood to cover the open areas similar to B.H. Davis.
Not sure if this applies, but we have a 5x10 bed and mostly run 4x8 sheets. I took 2 pcs of laminate and glued them back to back to make panels that cover the unused portion of the bed,that along with CV stay down cutting have reduced my lost parts to almost 0. 18 hp becker pump with 3/4 ldf spoilboard and 1/4 ldf wasteboard.
You are already invested in your machine but from what i've experienced, roller hold -down CNC's are specifically made for frame cutting. Most companies with these machines even stack cut a few sheets in one shot. Any major cnc router manufacturer has roller hold-down as an option.
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