LumberJocks

Forstner bit

  • Advertise with us

« back to Woodturning forum

Forum topic by Karda posted 02-03-2018 10:57 PM 1026 views 0 times favorited 29 replies Add to Favorites Watch
View Karda's profile

Karda

1103 posts in 576 days


02-03-2018 10:57 PM

Hi, I want to use a little larger than 2” Forstner bit to make the recess for my bowl blank but my drill press has a minimum speed of a little over 500 RPMs is that slow enough for that large of a bit thanks Mike


29 replies so far

View Rayne's profile

Rayne

910 posts in 1562 days


#1 posted 02-03-2018 11:17 PM

Found this. I’ll keep this around for myself as well. lol. 500 for softwood and 250 for hardwood.

Drill Press Speed Chart

View msinc's profile

msinc

421 posts in 526 days


#2 posted 02-03-2018 11:23 PM

No, it is my experience that 500 rpm’s is not even close to slow enough. I use Forstner bits for old work plumbing to drill thru studs. I have them both smaller and bigger than what you want to run. Milwaukee makes a heavy duty angled drill motor called a “plumbers hole hawg” just for this. To safely drill holes this size with this type bit it crawls it is so slow. I just checked the published rpm’s of the drill and it is variable speed 0-330 rpm. You can change the little gear box to go up to 750 rpm, but I have never been able to use it full throttle on the low setting. Most of the time I am using it I probably do not exceed 100 rpms or it will hang up and hurt you.
My drill press will go down to 250 rpm and I don’t think that is slow enough.

View Lazyman's profile

Lazyman

2038 posts in 1410 days


#3 posted 02-03-2018 11:44 PM

Not saying it is safe, but what I have done is first drill the hole with the the largest bit that is rated at 500 RPM and then drill the rest with the larger bit and go very slowly, backing out frequently. My logic is that at least it wasn’t doing quite as much work but it might still result in a disaster so try at your own risk. I’ve done this on the lathe using a Jacob’s chuck in the tail stock of my lathe as well. Maybe I’ve just been lucky but no problems yet.

Note that on the drill press, before I drilled with the smaller bit, I use the larger bit first to scribe a ring so that I could easily line up the large bit with the ring since you are losing your center point.

Another option that I haven’t tried is perhaps to mark the 2” circle and drill it out the area with multiple holes to clear out most of the waste and then just use the Forstner to clean it out and get a flat bottom. Again try at your own risk.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

View johnstoneb's profile

johnstoneb

2932 posts in 2195 days


#4 posted 02-03-2018 11:50 PM

Clamp everything down tightly and very slow feed. The big danger is the bit grabbing and taking the work for a nasty ride and you with it. clamp it down tightly.

-- Bruce, Boise, ID

View Lazyman's profile

Lazyman

2038 posts in 1410 days


#5 posted 02-03-2018 11:57 PM



Clamp everything down tightly and very slow feed. The big danger is the bit grabbing and taking the work for a nasty ride and you with it. clamp it down tightly.

- johnstoneb

+1. Forgot to mention that.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

View Dark_Lightning's profile

Dark_Lightning

3163 posts in 3131 days


#6 posted 02-04-2018 02:01 AM

Depending on how big you want to go, you can use a hole saw and then pry the plug out. It’ll blow out some of the wood below, so you might use some caution with that- just don’t drill too deeply. I guess with a hole saw, you won’t be boring that deeply in one pass, though. This will only work if the wood grain is across the piece. If you are stacking the pieces, you can drill all but the bottom one and use a scroll saw to cut out the “waste”. I bought a plank of mahogany, and made 3 bowls out of it using this method- 14”, 10” and 7” diameter bowls from one bunch of wood. Laid up sections with the grain running perpendicular to the one below. There will still be waste, but a lot less than just hogging it out.

Note- as Bruce said above, just use a slow feed rate. In the machining biz, the concept of “surface feet per minute” applies. There are guidelines on how fast you can cut, based on the amount of surface that is going to be removed, and the difficulty of the material being cut.

-- Random Orbital Nailer

View Karda's profile

Karda

1103 posts in 576 days


#7 posted 02-04-2018 02:21 AM

thanks I won’t be drilling deep, this is for a recess for my chuck, 1/4 – 3/8 deep

View IantheTinker's profile

IantheTinker

237 posts in 149 days


#8 posted 02-04-2018 02:23 AM

I am glad you asked this question, Karda. I for one constantly forget to change the speed of my drill press for different woods. This was a good reminder.

-- “How you feeling, Roy?”... “a little unappreciated, Al...” - Die Hard

View Nubsnstubs's profile

Nubsnstubs

1296 posts in 1752 days


#9 posted 02-04-2018 03:44 AM



thanks I won t be drilling deep, this is for a recess for my chuck, 1/4 – 3/8 deep

- Karda


You give up on tenons???.......... Jerry (in Tucson)

-- Jerry (in Tucson) www.woodturnerstools.com

View Karda's profile

Karda

1103 posts in 576 days


#10 posted 02-04-2018 04:02 AM

Tenons are messy. I have developed a liking for footed bowls. They look nice and are east to hold but when I am down to a stub I can’t cut them out with out messing up the foot and a chisel is questionable when the wall is this. I like the look of a well cut recess and the bowl bottom is finished. Also I think a recess is better on something thin where there may not be room for a tenon I wouldn’t say givin up just want to learn new options

View Lazyman's profile

Lazyman

2038 posts in 1410 days


#11 posted 02-04-2018 05:55 AM

If you have a wood worm screw for your chuck, just mount the bowl blank backwards and use a gouge or carbide tool to make your recess.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

View Karda's profile

Karda

1103 posts in 576 days


#12 posted 02-04-2018 06:01 AM

but that is not teaching me how to do a recess, besides I have a hard time getting worm screws tight because my lathe doesn’t have a spindle lock. I want the recess for times when I don’t have room for a screw or face plate. I just then in. i thought a bit would be faster.

View MrUnix's profile

MrUnix

6760 posts in 2221 days


#13 posted 02-04-2018 08:02 AM

Just for reference, none of my lathes have a spindle lock, and mounting on a woodworm screw is not an issue in the least. And it doesn’t matter if you don’t get it super snug at first, as it will tighten up by itself as soon as you start turning anyway.

Cheers,
Brad

PS: Never had a time where there wasn’t enough room for a glue block :)

-- Brad in FL - In Dog I trust... everything else is questionable

View Lazyman's profile

Lazyman

2038 posts in 1410 days


#14 posted 02-04-2018 02:17 PM

No spindle lock for me either. Just use the same tool you use to hold the spindle as you remove a chuck or face place and tighten as much as you can by hand. It just need to be snug enough that it doesn’t pivot or wobble on the screw. It is actually harder to get the block off without a lock than on (since it tightens as you turn).

I find it easier to rough and shape the outside, flatten the bottom and also add the tennon or recess with it mounted on a wormwood (quicker than a glue block but that works too). Once the bottom is flat and the blank is round. cut a recess with your tool of choice. In fact if your chuck jaws have a dovetail profile, it is best to make the recess, or a tenon for that matter, dovetailed as well to get a good solid grip on it when you remove it from the wormwood and remount it on the chuck. Another advantage of using the wormwood is that you can drill the hole for the screw to just slightly more shallow than you want to hollow and give yourself a guide to where to stop the roughing phase.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

View LeeMills's profile

LeeMills

549 posts in 1323 days


#15 posted 02-04-2018 04:08 PM

As to bits. Look at the chart again and go down to Multi Spur bits 2-1/8 – 4” , 250 rpm. I use a 3-1/4” often to set the area for my 3” faceplate or 50mm or 70mm jaw top with the worm screw. I would do as other suggest and clamp the work to stay centered and start smaller and work up.
That said, if concerned with thin work I would not use a bit as is. You have to remember how deep the point will also cut which may be quite a bit. I have heard of folks regrinding the point but I do not have that skill.
You may be able to start with a small (3/8” forstner) which would have a short point and just grind the point off of the larger bit.

As an alternative, when forming the initial recess I only remove enough for the chuck jaws, usually about 3/8” wide and deep. It doesn’t make one bit of difference if the center of the recess is removed at this time or not. This allows room to cut the recess without the live center getting into the way. You still have your center point for remounting.

Cleaning up the recess at the end is quick but I did spring for Vince’s 1” sanding disc. The nub I leave is usually about 1/4” to remove by cutting/sanding.

-- We cannot solve our problems with the same thinking we used when we created them. Albert Einstein

showing 1 through 15 of 29 replies

Have your say...

You must be signed in to reply.

DISCLAIMER: Any posts on LJ are posted by individuals acting in their own right and do not necessarily reflect the views of LJ. LJ will not be held liable for the actions of any user.

Latest Projects | Latest Blog Entries | Latest Forum Topics

HomeRefurbers.com