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Need help w/ drill press / Forstner bits

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Forum topic by mzgodinski posted 01-28-2019 10:48 PM 600 views 1 time favorited 12 replies Add to Favorites Watch
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mzgodinski

5 posts in 525 days


01-28-2019 10:48 PM

Topic tags/keywords: drill press forstner bit

Hey guys,
I’m new to the Lumberjocks Community, in the sense that I’ve never posted anything before.
I’m an amateur wood worker, and recently bought an inexpensive drill press. I also bought a set of Forstner bits at the same time. The Forstner bit packaging did not clearly state anything about MAX RPMs, and anyways, I assumed Forstner bits were generally for use in drill presses.

I’ve assembled my drill press (5 speed), and learned that the range of speeds at which it can drill are from 760 – 3070 RPM. Thus, I was dismayed to find that all of the forstner bits in the set I purchased have max RPMs of 500 or less (these were printed on each individual bit).

Can anyone shed some light on why these Forstner bits cannot be used in this drill press, and what the importance of max RPMs is?

My intention is to drill an approx 1” hole in some 1/2in thick polycarbonate sheeting.

Can I use a spade bit at the RPMs that my drill press runs at?

thanks,
matt


12 replies so far

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syenefarmer

540 posts in 3585 days


#1 posted 01-29-2019 12:18 AM

This chart, http://images.meredith.com/wood/pdf/drill-press-speed-chart.pdf , has been very helpful to me for many years. If you want the best result when using whichever drill bit you happen to be using this has always been spot on for me.

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pottz

6301 posts in 1489 days


#2 posted 01-29-2019 12:50 AM

great chart i just printed it out and will post by my drill press,although i have to admit ive never changed the speed since i bought the press several years ago,but for the best performance from a given bit i probably need to start.thanks for posting this.

-- sawdust the bigger the pile the bigger my smile-larry,so cal.

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Holbs

2242 posts in 2534 days


#3 posted 01-29-2019 12:58 AM

Dinski.. I had the same issue when I first started out wood working. Had a 5 speed 10” drill press and forstner bits. Didn’t quite understand the RPM requirements and blue color came from it.
As I now understand it… larger the fortner bit, the more heat generated because of the larger square area contacting the wood creating friction heat. To combat this, slow RPM’s are needed to generate less heat.

-- The Carpenter Bee is derived from the Ancient Greek word wood-cutter "xylokopos/ξυλοκὀπος"

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mzgodinski

5 posts in 525 days


#4 posted 01-29-2019 01:35 AM

Thanks everyone! I appreciate the chart and your experiences w/ Forstner bits!

View ArtMann's profile

ArtMann

1432 posts in 1320 days


#5 posted 01-29-2019 03:26 AM

I don’t necessarily pay any attention to the official recommendations. If the slowest my drill press would go was 760 RPM, I would use the Forstner bits anyway. I would just take it slow. If your drill press is weak like a lot of like a lot of the 5 speed machines are, then your worst problem may be stalling.

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derosa

1597 posts in 3340 days


#6 posted 01-29-2019 04:30 AM



I don t necessarily pay any attention to the official recommendations. If the slowest my drill press would go was 760 RPM, I would use the Forstner bits anyway. I would just take it slow. If your drill press is weak like a lot of like a lot of the 5 speed machines are, then your worst problem may be stalling.

- ArtMann


I’m inclined to follow this, in part based on the experience of just being too lazy to change the belt position every time. I’m actually going to print out the chart above and post it as well but with forstner bits which I only use from 3/4” and bigger, I just always made sure the RPMs were below 1000. Doubt a good bit would come apart, just burn, but slow and steady with pushing into the wood can offset the difference in speed.

-- A posse ad esse

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Madmark2

508 posts in 1093 days


#7 posted 01-29-2019 08:07 AM

Use carbide forstners instead of HSS . . .
M

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TheFridge

10859 posts in 1990 days


#8 posted 01-29-2019 02:26 PM

Just take your time and peck if the speed is a little too high even at the lowest it’ll go. If it starts smoking, it’s already too late.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

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them700project

170 posts in 1523 days


#9 posted 01-29-2019 02:41 PM

Hah I sought this chart out and printed and laminated it about an hour before the original post

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mzgodinski

5 posts in 525 days


#10 posted 01-29-2019 10:38 PM

Thanks! I’ll maybe try a Forstner bit at 760RPM and let you know how it goes.

View MPython's profile

MPython

166 posts in 317 days


#11 posted 01-29-2019 10:52 PM

Be careful drill polycarbonate. It can be “grabby” and the bit can snatch the workpiece out of your hand with unpleasant consequences. Otherwise, I agree with the advice above: use the bits in your drill press and go slow.

View Ocelot's profile

Ocelot

2347 posts in 3142 days


#12 posted 01-29-2019 11:03 PM

How thick is the polycarbonate?

You might do just as well with a hole saw.

The forstner bits have a point in the middle that engages first, teeth on the rim that engage 2nd, and two chisel-like parts which engage last. Those last parts do the most cutting and are not needed if you are making a through hole. For that case, a hole saw will work – if in relatively thin material (less than 1 inch or however deep the cup of the hole saw is), and will take a lot less power and produce less chips than a forstner bit.

But… hole saws are not usually as nicely toleranced in the diameter. So, if you need a tight fit, Forstner bits may be the only way.

I have used Forstner bits up to 2 inches in my little DP (like yours) at 660 RPM. Go very slowly or it will for sure stall.

Yes, and clamp your workpiece for sure.

-Paul

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