Limits to Vacuum When Routing Small Parts

A newcomer asks what size parts he should expect his vacuum table to manage. Experienced hands discuss his problem. July 2, 2005

We are about 3 weeks into a new router with a 500 CFM vacuum pump on a 5x12 table, 5x4 of which we have blocked off with a piece of laminate. My question is, how small of a part should I be expecting to "lose" to inadequate vacuum?

When placing a 5x8 onto the remaining table area, I am losing parts that are 60 square inches or less - is this to be expected?

These are onion skinned and in fact we have set our parameters at what I consider oversized, to skin anything that contains any edge under 5" or a square inch area of less than 100. My gut is telling me something is wrong here.

Forum Responses
(CNC Forum)
To the original questioner: Inches vacuum? Type and thickness of spoil board?

To the original questioner: Also - cutting tool, rpms and feed speeds? Material being cut?

From the original questioner:
We are using only a 3/8 mdf spoil board which has been surfaced both sides, cutting tool is a 1/2 comp. Onsrud cutter @16,000 rpm 750 inches per min. cutting 3/4 white melamine, or 3/4 particle board laminated both sides.

From contributor B:
We have a 5 x 8 Northwood with a 40hp vacuum pump, and we cut 3/4 melamine at 700ipm with a 3/8 2-flute vortex comp cutter. We onion skin all parts to help reduce part movement and we get the parts and table quite clean with the dust collector on the second pass. This does create some tool life issues.

We used to climb cut the parts, but we recently had someone tell us that climb cutting shortens the tool life, so we switched to cutting against the rotation. We started having some part movement, and small cutoffs like toe kick notches became projectiles, so we switched back.
In a mixed nest of parts we have no movement on parts as small as 15-18 square inches.

From contributor M:
I was also told to conventional cut, but seem to have better holding of parts with climb cut. What are others doing?

From contributor E:
In our material (3/4" ply) we find the quality of cut with a 3/8" comp. Spiral is only acceptable with a conventional cut. Some of our nests hit close to 40 parts per sheet. We finally adopted using bridges or tabs to hold the parts together as a sheet and then trimming with a laminate trimmer on a sorting table.

From the original questioner:
Thanks everyone. One thing we have discovered is my base is not flat, there is a joint line in the middle of the table and this joint is not level. This is causing air to enter between the table and spoil board.