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

[eaglesplsh]

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!

[jseiler]

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

[scott_smith]

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

[eaglesplsh]

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?

[stevem]

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

[bleeth]

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

[elcruisr]

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.

[Brady Watson]

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

[eaglesplsh]

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!

[Brady Watson]

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