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

We leave cut tabs (I've heard some call them bridges) around the perimeter of our parts to hold them in place while machining.

I'm looking for a better tool/method to cut through these tabs (cutting the part away from the surrounding scrap) and to trim the tabs off the parts after the CNC machining is complete.

Our best solution so far has been diagonal cutters (wire cutters) to cut through the tabs and a flush trimming router bit for trimming the tabs off.

We only cut panels 2'x4' or smaller, so we can take the panels off the machine and flip them over for easy access to the tabs. But, I'd like to get a larger machine that cuts full sheets of plywood/plastic. I don't think a 4'x8' panel full of small parts could be removed from the machine without it falling apart. (Anyone doing this currently with repeated success?) I can't figure out how you guys with full sized machines cut through your tabs with the panel still on the machine. We use a 1/4" diameter bit, so the slot is too narrow to get our wire cutters into for cutting the tabs from the top side.

The other problem with using wire cutters is that your hand hurts after cutting 100's of tabs.

I'm sure that someone has found a better method/tool. We'd sure appreciate hearing about it!

I can't remember where I got mine (it might have mlcs woodworking), but here's something similar. I run it in a $30 harbor freight laminate trimming router. works great.
I didn't come up with idea myself...someone posted it here on the forum.

http://grizzly.com/products/Solid-Ca...-4-Shank/C1455

Its a 1/4" flush trim laminate bit. It will follow a 1/4" groove cut by a 1/4 endmill nicely and quickly knock out those tabs. I find laying the piece I'm cutting on a non-skid mat (I use rubberized shelf liner) really helps keep the pieces from shifting until everything is cut out.

John

I use the same bit as John except I Jig saw the full panel as it comes off the bot into manageable size “pallets” of parts and use the router table to free the parts. I suppose you could use the bot to cut the sheet into ¼ sheets after the parts are cut if hold-down was sufficient.
Scott

Thanks for the info!

I spent at least an hour trying to search the forum for this type of info before posting my question - too many other posts about cut tabs instead of "cutting through cut tabs" in post processing. I just did a search for "laminate trimmer" and that brought up a bunch of similar posts to those in this discussion.

Sounds like everyone who trims tabs this way flips their sheet of parts over to get at the tab (bottom) side for trimming. (Unless they're using a router table as discussed above.) I'm still interested in hearing from folks who are cutting 4'x8' sheets into a zillion small parts - what's the trick for flipping sheets over without everything cracking apart at the tabs? Do you leave a wide web between parts? How wide? What about on 1/4" and thinner materials that flex a lot?

Have you tried capturing your cut sheet between two uncut sheets and flipping all three at the same time?

Russ- Try an overhead bearing (pattern) bit. No flipping required.

We cut 4x8x.75 sheets into small parts all day! Usually upwards of 40 parts but some jobs we cut 60. Steve M is on the right track for our tactics. We pull the sheet off whole onto an outfeed table over a 4x8 of cardboard or 1/4 ply. Sandwich it and flip. We do all our cutting with a 3/8 tool when possible so a 1/4" laminate trimmer does the job for us.

Russ,
You might want to look into another hold down solution, such as vacuum. There are many shoestring budget solutions proposed on the board for using vacuum to hold down parts using nothing more than a good shopvac. You might want to look at the 9-15 Open Source Vac Project & other similar threads.

I started on my CNC using tabs & screws, only to find that I was spending more time monkeying with breaking parts out of the scrap than it was worth. Only when I switched to vacuum did I realize just how good life could be
I've held down parts as small as 1/2 X 3/4" with a single Fein T3 vacuum, a well thought out vacuum jig & some AllStar gasketing. No tabs. No cutting. You just turn off the vac and swap out finished parts for a new blank & do it again.

Investing in vacuum will save you money...In the meantime, a 2" sheet of EPS foam on a set of horses (with 2X4s under for support) and a jigsaw will work well for breaking out tabs. Just place your finished sheet on the foam and cut out your parts. The foam will keep the jigsaw blade from getting jacked around when you cut thru, but still support your sheet.

-B

Ironically, I spent hours reading about the 9-15 Vac Project just before Brady's post.

I knew someone was going to bring up vacuum clamping - it couldn't be helped!

I actually started with vacuum clamping 3 years ago. Bought several types of gasket from AllStar and a vacuum pump, etc. I had just bought the CNC machine and was trying to learn the software, hardware, tooling, materials, and clamping all at once. It was way too much to tackle in one bite. After a month of struggling with warped material that didn't want to make a good seal and a dozen other problems that caused my parts to get thrown across the room, I decided to try tabs.

I do use vacuum for some jobs, but bottom line is tabs work. They produce reliable consistent results for me. And the trade off in time between tab cleanup vs. creating separate vacuum fixtures + gaskets for each part seems about even when you aren't producing xerox copies in quantity.

I'm certainly going to look into vacuum again when we upgrade to our next machine. But I don't think I'll ever stop using tabs completely. It's one of those "right tool for the job" situations. (Ironic since that's the theme of this thread.)

I've got the laminate trimming bits described above coming today. If they're as helpful as I'm imagining, I'll be sure to report back to the group.

Thanks again to everyone for the good advice!

Russ,
There's no 'wrong method', obviously...Whatever works!

In regards to vacuum, many people have poor results using vacuum pumps. By 'pump' I mean ones that generate high vacuum & low CFM. They are only good for non-porous materials & are not reliable enough or have enough CFM to 'get over the hump' when cutting sheet goods. A higher CFM solution, such as the 9-15, would allow you to cut parts, in MANY cases, without gasketing at all. Since I developed the BradyVac II grid system, I have not had the need to buy any AllStar gasketing, or other brand for that matter, when cutting smaller parts. If you have enough CFM, then you can use a universal bleeder board, like the BradyVac I, or similar, to suck down any shaped part without a fixture. There is a performance hit without a dedicated fixture, but I think that you would find the results worthy of a time & money investment...most likely when you get tired of cutting tabs
A few sheets here or there is fine...but if you get a job where you have to cut 300 sheets, it gets ugly...and frustrating. Ask me how I know...

-B

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

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...

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

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

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.

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

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.

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

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

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.

Quote:

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Originally Posted by 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.

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How do you cut the tabs afterwards, Steve?

Quote:

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Originally Posted by asteude

How do you cut the tabs afterwards, Steve?

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no tabs I use a downcut bit of the right size so the sawdust holds the part in place.
here is a sample the circles were cut out of 1/4" bb ply with a 1/8" downcut one pass. the other parts were cut out of 1/8" bb ply one pass a 1/16" downcut bit. This works well but it depends on the plywood/material the size of the bit number of passes. But seldom do I need tabs but it may slow cutting down. but you don't have to clean the tabs off or cut them either.

http://i154.photobucket.com/albums/s...g/dd5cb66c.jpg

I've been looking around trying to find some tab cutting solutions. I'm working a vacuum system, but imagine I will still need to use tabs on occasion and would like to have a good method in place.

I was thinking back to my earlier woodworking days before I had any of those fancy flush trim bits with bearings. I would just use 1/4" or 1/2" straight bits and let the shaft above the cutting length be the bearing surface on the pattern. It got me by.

So why not just use 1/4" spiral cutter bits with a short cutting length (like 1/4") in a laminate trimming router to cut the tabs from the top on 1/2" or better material?

I don't know-Why Not?
Actually if I am going to use a router and did my object cutting on the bot with a 1/4" bit I don't like having to "shove" a 1/4" bit in a hand router in the slot.
Although I don't do tabs often, for wood, depending on the thickness and size/shape of the pieces, I may use a router, knife, razor, Japanese dovetail saw, or chisel.

I see your point about needing to undersize your tab cutting bit, compared to slot size.

I have been searching for a spiral 1/8" DIA bit with a 1/8" and a 1/4" cut length. I have found some with 1/4" cut length, but not 1/8". The thing I am concerned about is that the machining of the bit extends well past the cut length, which gives you less room for error on the finished surface.

Don't like to use tabs as well but sometimes still best for small parts, I cut it out with jig saw with fine blade or a vibrating multitool with a slim attachment for sturdier parts or a wood cutting disc on a Dremel for delicate ones. Or, I cut the tab so thin that I can break it out without tearing. I wish I had not sold my scroll saw since that might be the cleanest and least damaging way for small stuff.

I use a 3/16 flush trim bit in my trim router.

I use a Rotozip to cut my tabs. Since I use a 1/8" sacrificial board under my material, I can set the Rotozip bit to cut just barely through and the tabs and skins cut very easily.

I use a Harbor Freight oscillating tool (used to be called a "Fein Tool" before their patent ran out) with a Bosch 3/8" Wood/Metal blade to cut the tabs, then take it to the table router with a piloted trim bit to smooth them off.

A Dremel tool cutoff wheel works well for some items, you want to locate the tabs so they are easy to cut.