Best tool for trimming / cutting through tabs or bridges for post CNC processing

[pappybaynes]

Brady,
If I read your post correctly, you are saying that the vacuum pumps will not hold down a sheet of cabinet grade plywood well enough to cut cabinet parts out??
Dick

[eaglesplsh]

At the risk of forever pushing this discussion off topic...

Brady, I went back and reread your article on the BradyVac I and II grid system - glad I did. My first read was a month or two ago and I must have read things too fast. At the time I remember thinking that BradyVac I was the universal hold down that everyone has wanted for a long time - if it worked with a cheap vacuum source. From the BradyVac II addition, I jumped to the conclusion that BradyVac I wasn't working with a cheap vacuum source, so you were going the standard strategy of improving the seal. I saw the pictures of grooves and the one picture of gasket tape (on the bottom of the fixture) and started remembering my nightmares.

With the reread and reading the 9-15 posts I'm now under the impression that BradyVac I does work for many parts with the 9-15 vacuum source. (Please let me know if I've got that wrong.)

Most of my jobs are one-offs. Repeat work gets run once per month at most, a couple of sheets at a time - hence my hesitation toward designing, building, and storing/maintaining a lot of custom vacuum fixtures. But I can see the beauty in using a combination approach - Universal hold down by itself when it will work, Universal hold down with small parts tabbed for one-offs that need it, custom fixtures for repeating production runs with small parts.

Sounds great in theory - and the 9-15 parts are so cheap I almost can't say no to trying it. Now if only I had the time...

[harryball]

I use 1" tabs, a 1" chisel, a deadblow mallet and my 12 year old son. ;-) Just place the chisel flat against the part, one quick whack and move to the next one. If I need to clean the part I use a laminate trim bit on my router table or my spindle sander depending on the desired finish quality, material etc...

/RB

[Brady Watson]

Russ,
Vacuum has a lot of potential and something as simple as a single Fein ShopVac can hold down nearly anything, if you make full use of the vacuum you have. I held down the small parts with just the Fein, and hold down full sheets of plywood with a single Fein, a BradyVac I (grid milled in back side of Trupan) and run some foil tape around the edges. It isn't on par with a huge regen vac, but it also isn't as loud, hot or expensive to run. Careful toolpath preparation will pay dividends when cutting with 'vacuum on a shoestring'. I freely take the BradyVac I off the table and store it when not needed. I also have several BradyVac II purpose built fixtures for when customers call to re-order specific parts. It is rare that I use screws, tape or clamps to hold anything down anymore...I've been spoiled by vacuum & the increased cut quality that it brings to the table. It's worth a looksy...

-B

[eaglesplsh]

To help out others that might stumble across this info in the future, I thought I'd summarize our findings after testing out a lot of the advice given in this thread.

The 1/4" flush trim bits with the half-round bottom pilots work great for trimming tabs. Definitely the best option we've used so far. The cheapest source we could find was Eagle America, who sells the bits in single and double ended versions. They also sell a version that has a flat bottom instead of the half round – could be useful for thin materials or materials with tabs that are next to pocket cuts (making a thicker material effectively thin.)

The bits do have some restrictions that other tab trimming methods don't, so keep these things in mind:

1. Your tabs need to be less than 0.200 thick. That's not a problem for most materials. We ran into this when we were using a ball mill to cut parts and didn’t want to switch bits for making the profile/tab cut. At their lowest point the tabs were .125 thick, but the ball mill left a 1/8" fillet where the tab connected to the part. The fillet + tab was too thick to cut with this type bit, so we went back using a regular full-size flush trim bit with ball bearing in our router table.

2. Your material needs to be at least 3/8" thick to use this bit in a hand trimmer or router (cutting from above.) Prior to using this bit, we had trimmed our parts on a router table. Cutting them from above is MUCH faster, but the bit sticks down too far to use it on 1/4" parts, etc. This bit is still the best option we've seen for thin materials when used in a router table because the bearing “rides” flush with the cutter (as apposed to ball bearings that ride 1/10 or more above the cutter with a washer in between.)

I'd recommend using a router with a clear base - makes it MUCH faster to maneuver around all those parts. A router with built in dust collection is really nice. At first I thought we’d want a small trim router, but we think a full size router, with 2 hands for control, allows us to work faster. The clear base allows you to see what you're doing when moving the bit from one part profile to another. This can really save you time because with this bit there's no need to turn the router off and wait for the bit to stop spinning between cuts. The bit’s round bottom tip doesn’t mar the finish on most materials - even if you miss the profile slot and accidentally touch the part with the end of the cutter.

We found the rubberized draw liner works a lot better than the “carpet padding” style mats for holding our panels of parts in place while routing. The thin stuff keeps the parts aligned in a flat plain. The other stuff allows trimmed parts to tip while you’re trying to trim the rest of the panel. The “tipped” parts catch the base of the router making it hard to maneuver.

If you tab one part to another part instead of laying things out with webbing in between, make sure you’ve trimmed the tabs on both parts – Sometimes, when you run the router around the first part, you’ll leave 1/16” of the tab on the second part, which is hard to see when you’re moving fast and could be a problem when you go on to assembly.

As many have pointed out, if you have the time and money to develop a flexible and reliable vacuum clamping system, it could save you from having to mess with tabs all together.

Once again, we’d like to send a big thank you to everyone who helped us out with their advice and best of luck to those who may find this info useful in their own shops.

[pkirby]

I know this is an old thread, but it has some good points in it and I wanted to mention a new solution I found. Amana just started making a new flush trim bit that has a 1/4" shank but reduces down to a 3/16" cutting diameter. It's perfect for cleaning up tabs that have been cut with a 1/4" cutter. It also has a mini bearing so it rides smoothly. The tool number is MR0102. I recently bought it and has worked well, but I can not speak for the longevity of it because I haven't used it that much. PS...I'm not affilitated with them.

http://www.amanatool.com/bits-fv/mr0...flushtrim.html

[asteude]

Paul, that is the perfect bit for this job as long as the sheet you're cutting is still sturdy enough to flip without breaking apart. (I don't have enough room in my shop to do the sandwich method.) Thanks for posting!

RB's method seems like an easy solution, but I quickly found out that (a) 12 year olds tend to wander off and (b) using a chisel to cut tabs tends to blow out the back of the material (especially with plywood.)

I primarily use two methods:
1. jig saw - after unscrewing the cut sheet, I start pulling it off the table and saw through the tabs as they clear the spoil board. This is a bit unwieldy with larger parts and a bit scary with smaller parts (since I have to hold them with my hand as I cut.)
2. multi-tool - I use an oscillating multi-tool (mine is a Porter Cable) with a saw blade. This is pretty rough on the spoil board. I haven't gotten around to trying to slide a piece of protective plywood under the cut sheet. This method is pretty loud and tires the hand pretty quickly. I also sometime mar the cut parts if I get sloppy and miss the groove. But otherwise, it's safer than the jig saw.

[asteude]

I just also found the 1/8" version of that flush cutting bit: http://www.amanatool.com/bits-fv/46197.html

This 1/4" bit might work OK if you can't flip your cut sheet. In my case, the cut is 1/4" wide and the cut edges are very visible in the final product, so I can't risk burning them by getting the bit stuck trying to cut tabs.

I think the perfect solution would be a 1/8-3/16" template bit. If anyone finds one of those, please post here!!

Andy

[bobmoore]

I use a jig saw also but I turn the speed way down. More control of the cut and much safer. sand flush and you are done.
Bob

[knight_toolworks]

even without a vacuum if you use the right size downcut many plywood and materials can be cut without parts shifting. it's rare when I need tabs for anything. I cut these pretty small parts from 1/8" Russian plywood 1/2 half sheet 30x60 takes 3 hours to cut with a 1/16" downcut bit but the parts stay in place. I added tabs so they would stay in the sheet when I cut the sheet into parts.