Annular cutters or drill bits?

tjb

tjb

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Hello, All.

I need a little wise counsel. I need to mill a series of holes in 1/4" white acrylic. The holes will be 1", 1 3/16" and 1 3/8". I have a 1" Silver & Deming drill bit and have already milled that set, but I'll need to buy tools for the two larger sizes. Using my rotary table for the larger holes is not practical because there will be 20 or 30 for the complete project.

There was some recent discussion in another post about annular cutters which caused me to wonder. Since I need to buy one or the other, which makes more sense? Larger drill bits or annular cutters? Neither will be cheap, but based on a cursory examination, cost seems to be relatively similar either way. I drilled the 1" holes in two steps - 1/2" followed by 1" - with no issues. Would the process be the same with annular cutters or can it be accomplished in a single step?

In addition to the immediate project, another consideration would be which would be more sensible to have lying around in a tool box for future uses which may arise in different media (aluminum, cold rolled, etc.).

Any thoughts?

Regards,
Terry
 
Generally you shouldn't use regular drill bit for acrylic, especially for thin sheets. They tend to grab & will crack the acrylic as you get close to punching through. Using material to back it up helps a lot. Modifying the cutting edge on the drill bit to prevent grabbing like how you modify for drilling brass is another trick too. Laminate drill bits are what you are supposed to use but they are expensive. Not sure if they even have sizes that large.

I haven't used an annular cutter on acrylic but I have been using them a lot more lately rather than S&D drills on the lathe. They're very sharp so they should cut well but the have a very positive cutting edge so they may grab also. Annular cutter are much more expensive than S&D drills though, well unless you buy on ebay. :)
 
Annular cutters are expensive, both to buy and to sharpen.
 
I would think you could make your own annular cutters for use on acrylic? The material does not need to be that hard. You could optimize the tooth design to not grab the material.
Robert
 
What about using the forstner bits for wood? I think they would help with the breakout issue, and cheaper then the annular cutters.
 
If your tolerance allows, I'd use hole saws. If tight tolerance then use the Forstner bits, they work good on the white cutting boards I use for fixtures.
 
Thanks to all who have answered so far. On the 1" cuts, I have had zero chip issues on 32 holes. I started the first 8 with a 1/2" bit, stepped to a 3/4" and finished with the 1". On the second set of 8, I skipped the 3/4" step and still, no chipping. Finished the last 16 that way with no issues. I have my mill set at 600 RPM and hand fed the first set very slowly. For the remainder, I had my quill feed set at its slowest speed, and it worked like a charm. Time consuming, but uneventful. Before starting, I sharpened the point on the 1" bit and tested it on scrap to make sure there was no grabbing.

Did I get lucky, or is a single intermediate step and slow speed the right combination? I feel pretty good about using larger drill bits - especially if I step up to them from the 1", but would annular cutters be better? Robert, I've never even been in the same room with an annular cutter, so making my own at this point is simply out of the question. Any opinion about store-bought annular cutters being an improvement over S&D drill bits for this application? Anyone?

Regards,
Terry
 
Grandpop said:
If your tolerance allows, I'd use hole saws. If tight tolerance then use the Forstner bits, they work good on the white cutting boards I use for fixtures.
Click to expand...
Tolerance needs to be a little tighter than what I would anticipate from a hole saw. I quick look on MSC shows a 1 3/8" Forstner bit, but not a 1 3/16". That bit is a whole lot cheaper than a standard bit. In your opinion, is it likely I'd get the same result as with the Forstner?

Regards,
Terry
 
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