Best method for cutting 1 1/8 holes in MDF

[da_mike]

Newbe question here. Shopbot is on it's way (almost). I'm working on my parts files.

I'm going to be cutting panels out of 3/4 melamine laminated MDF. They have about thirty 1 1/8th holes (all the way though). I'm planning on using 1/4 inch bit.

Here's my concern. If I cut out the 1 1/8th holes with a 1/4 inch bit I can just imagine small circular wood projectiles flying all over my shop.

Tabbing might work, but I think it will probably chip the melamine? A very, very, small chip would be OK, say a 1/16 inch max?

I could route out the 1 /18 inch holes, but I think that would wear out the bits very fast.

I've read on the forums that Forstner bit are out, but what about getting a 1 1/8th router bit? This would require a tool change, but with so many holes it might be worth it, if it would work?

The other option is to build an acrylic cage around the router to stop the flying pieces. Great for dust collection, but really doesn't seem safe.

Any advice would be appreciated.

Oh ya, I’m using the router, not a spindle.

-Mike

[wayne_walker]

Mike,
I cut 1 1/4" thru holes with a 3/8" bit in 3/8" ABS plastic. In a 48" x 96" sheet, I cut 162 holes and the bit holds up quite well. After roughing out, I do a cleanup pass. Everyone says that plastic is much easier on bits.

The cut out piece just kicks up and hits the dust collector shoe. Some are vacumned up and the remainder stay on the table. My shoe is in "BAD" need of replacement with one whole side out, so a fair amount are still on the table or fall into the cutout hole.

Just my 2 cents

Wayne

[gerald_d]

Your thinking is perfectly sound - those small cutouts are a big headache. Aside from the safety aspect, those small pieces jam the cutter and sometimes knock the router out of position, or off the rails. We would probably use a 1/2" bit and clear out all of the hole. Or, somebody will follow a 1/4" cutter with a push-down-stick.....

Edited after seeing Wayne's post:
The thicker the material, the more likely it is to jam the cutter.

[bleeth]

I had a job just like that a while ago in which I was making a huge stack of decorative panels for a railing system. As Gerald suggests I used a 1/2" bit to minimize the size of the leftover piece and also set up my toolpath to leave a skin and small tolerance for the last pass to handle. This left the cutout laying in the hole and also gave me a sweet round hole. I was cutting 3/4 wheatboard with veneer both sides and so used a compression bit and had no tearout whatsoever.

Dave

[jseiler]

Three idea come to mind if you must use a 1/4" bit.

1) A spoil board underneath your melamine. Drill the centers of each hole at 1.25" (.75"+.5") or so, fill the holes with dowels to hold the pieces in place as you cut. I've not done this using only one peg, but have done a version of this with 2 pegs per cutout. worked like a charm. the dowels are reusable too.

2) Don't cut all the way through. Drill one hole in the outside path to allow a hand opeation using a laminate trimmer (with lam trimmer bit) to blow out the circles. Should leave a chip free cut.

3) Build a fixture spoil board that allows the cut pieces to drop through. Depending on dust collection, this could be problematic.

I like Gerald's idea of using a larger cutter and avoiding the issue straight away.

John

[mziegler]

Here several more options for this problem,
1) rout the plugs to sawdust
2) remove the dust collector shoe so the plugs can pop up and then can be suck up by a shopvac hose that you follow the cutter
3) program a thin tabs to hold the plugs in place and then rout all the holes, then snap all the plugs out by hand and then rerouted all the holes a second time to get rid of the tabs. This method is very safe and the method that I would use.
4) if the plugs are big and heavy enough, then program a thin tab to hold the plugs in place and then program another toolpath to rout out the tabs, the plugs will not pop up because there is very little force to rout out the thin tabs that hold them in place.

Mark

[da_mike]

Thanks for all the ideas. I think I'll order a 1/2 inch compression bit. Even if I figure something else out I’m sure I'll use it in the future.

I've managed to just fix my fixture on one 4/8 sheet, but only if I use the 1/4 inch bit. So, I might end up using a quick change collet to make swapping out bits simpler.

Thanks again for the help. You guys have given me plenty of ideas to play around with. When I figure out what works best for me I'll try to post it here.

-Mike

[gerald_d]

Mike, a 1/2" compression bit is a beast of an expensive cutter. 3/8" is more general purpose and plunges easier. Watch your "ramped" entries (inclined plunge) with big cutters in small holes. You can minimise (maybe even cure) fly-out problems with good 3D toolpaths - don't just bang the cutter up and down.

Quick change collet? Not for a router as far as I know......?

[mikejohn]

Drill through the material in the centre of the hole with the 1/4" (6mm) bit.
Offset 1/4" (6mm) cut a circle.
Offset again a little less than 1/4" (5.25mm) cut another circle.
this gives a hole 1 and 1/8" or 28.575mm with a 1/4" bit.

...........Mike

[robert_cheal]

I really like all of the ideas about fixing fly-out problems. I have been frustrated many times with pieces getting caught and causing problems.
Now I have a few more ideas to try out. Its great to step back look at a challenge with the view of another person.