How do you use a large forstner bit?

[ken masoumi]

I was using the 3'' saw tooth bit from the kit: Grizzly H5982 (http://www.amazon.com/Grizzly-H5982-Forstner-9-Piece-1-Inch/dp/B0007D2C9C/ref=sr_1_1?ie=UTF8&qid=1432992187&sr=8-1&keywords=Grizzly%20H5982%20Forstner%20Bit%209-Piece%20Set,%201-3-Inch&tag=vglnkc7237-20) set ,used my drill press,low rpm (500 rpm) ,the piece of plywood I was cutting was well clamped but as soon as the tip of the screw touched the wood it grabbed on so hard that I had to shut the drill off to stop,so I manually loosened the bit and removed the center screw from it and continued to cut the 3" hole without the screw end.

I have been told I could just grind the threads and use it like a smaller size forstner bit but I really don't want to change the way this bit was designed, I thought about drilling a larger pilot hole first but is that how these larger forstner/saw tooth bits are used?
The center screw bit can not be any shorter than it is unless I cut the length of it, would that be a possible solution?
Here's the bit in question:
https://encrypted-tbn3.gstatic.com/images?q=tbn:ANd9GcTbUWFgvppal7Bf7c789Z5IGdiM2Tm-4nfrfNQjUEOPmGvhU_ayLA
314604

[Ted Reischl]

314605Usually a bit with a screw is NOT designed to be used in a power tool, as you have quickly found out.

Take a look at old time hand brace bits and you will see they have a screw in the center also. Helps pull the tool into the work, supposedly.

Regular forstner bits do NOT have a screw in the center, they have a very short nib with cutting edges.

Take a close look at the picture in this reply.

[J.R. Rutter]

The screw tipped self feed bits are made to use with big handheld drills for construction type jobs. And by big drill, I mean like a Milwaukee Hole Hog or similar design with a lot of leverage and heft.

[ken masoumi]

If I grind the threads and give the tip a sharp point/edge , it should work in theory.

[Greg R Bradley]

NOT a forstner bit. Looks like Grizzly is completely clueless.

Those are self feed bits and specifically designed for drilling holes in studs and joists in construction. Designed to be used in a hand held power drill. That shank can be used in a chuck but also in a standard 7/16" hex chuck.

Can't imagine trying to drill plywood but if you insist on trying, I would try 50 rpm, not 500.

[ken masoumi]

Thank you all for your comments.I bought this set never looking beyond the sizes and the price.
I just drilled a (slightly larger)pilot hole before using that bit and it worked very well.next step is to grind the tip and use it like a forstner bit.

[Tom M King]

As several others have already posted, it's a self-feed bit with that screw in the middle. The screw pulls it into the wood so the operator doesn't have to push so hard. More commonly calling "plumbing bits", and intended to be used in large, right angled, slow turning drills, like a Milwaukee Hole Hawg. It's not a Forstner bit. I'd complain and ask for the set to be returned.

[ken masoumi]

It's not a Forstner bit. I'd complain and ask for the set to be returned.
I bought them from Amazon a year ago to do a project but never got around to use them until now, "Amazon's 30-day returns policy" is long expired.

[Frederick Skelly]

I bought them from Amazon a year ago to do a project but never got around to use them until now, "Amazon's 30-day returns policy" is long expired.

Well, both Griz and Amazon have some flex in return policies, sometimes. I know for sure Grizzly does because they took back an item I didnt use 6 mos after I bought it. I paid the return shipping as a compromise. Both firms are reputable and if something is being incorrectly labled/sold, they should be notified. Heck, the owner of Griz often monitors this site and may even respond to this post.

But I urge you to call BEFORE you modify Ken. You can always modify them later.

Let us know what you decide to do and how it goes.

Fred

[Thomas Canfield]

I use 2-7/8" to 3-1/8" Forstner bits to make a flat spot for a faceplate or worm screw in chuck for turning, and often on very irregular hard wood. My Forstner bits do not have a center screw and the feed has to be very slow to avoid grabbing or beating, and the cutting edge has to be sharp. I use my drill press if possible, but for very large pieces a hand held 1/2" drill with brace has to be used and that gets even more exciting.

[ken masoumi]

Well, both Griz and Amazon have some flex in return policies, sometimes. I know for sure Grizzly does because they took back an item I didnt use 6 mos after I bought it. I paid the return shipping as a compromise. Both firms are reputable and if something is being incorrectly labled/sold, they should be notified. Heck, the owner of Griz often monitors this site and may even respond to this post.

But I urge you to call BEFORE you modify Ken. You can always modify them later.

Let us know what you decide to do and how it goes.

Fred
Maybe I should first try to find out if I can exchange my set with an actual forstner bit set.
Great advice,thanks fred, I'll update if I hear anything.

[Mike Cutler]

Ken

Good advice from all, but when you do finally get a real Forstner bit in that size, 500 rpm is going to be a little fast. There is a lot of mass in a bit that size. Forstner bits are slow speed bits, so you'll need to feed it slow and back it off, then repeat unless your drill press will drop down in rpm quite a bit.
I can't help but ask if a holesaw isn't more suited to what you are trying to accomplish with that bit.

I wouldn't bother grinding down that screw bit. Those are very aggressive bits and are designed to clear large chunks of softwood waste.

[John Lankers]

You found the solution yourself by drilling a pilot hole. I would try to get an exchange for the set before taking the bits to the grinder as well. But then, a good quality 3" Forstner bit can cost some serious money too. http://www.leevalley.com/US/wood/page.aspx?p=63566&cat=1,180,42240,63566 (example only)

[ian maybury]

As John - just go carefully in terms of the quality of what you buy Ken if you go down the new route. It wouldn't be hard to jump from the frying pan into the fire. Can't speak for what's on the US market, but having been down the road of a set of Eastern made Forstners i ended up putting out for some good ones. It's no fun when one cuts, the next doesn't, the next off only one side as a result of incompetent grinding of the cutting edges. Plus very poor steel. Colt and Famag are excellent if expensive (consistently clean entry and exit on even construction ply), but maybe there's more economical ones if you know exactly which to buy. Definitely not a product to buy unseen/unreferenced unless going up market.

As often said here it's advisable when possibe to use large Forstners in a drill press - or at least to take a lot of care to hold them accurately vertical if using a hand drill. The problem is that with the large diameter even a tiny tipping out of vertical will cause them to grab to one side, and the long lever may then displace the centre - with the possibility of its having first dug in and caused some splintering.

The type with the very short point/pip in the centre are not the easiest to centre on a mark anyway - it's very hard to see what's happening on the bigger ones. It's sometimes helpful to drill a shallow small diameter starting hole to enage the pip. There may be something going for the variety equipped with a centre twist drill, maybe somebody who has used them can comment? Can the drill be replaced with a short tip or the drill be removed for drilling blind holes?

[ken masoumi]

Great comments ,thank you all .
Ian, I have not explored the possibility of replacing the center screw bit with a twist drill bit but it is possible ,I'll have to look in to it if I don't hear anything positive from Amazon or Grizzly .
The twist drill bit will need to be cut to length and I'll have to grind a flat spot on it's shaft so the set screw on the forstner shaft can get tightened against it but overall it is a good alternative to grinding/reshaping the center screw,great suggestion Ian, thank you.

[glenn bradley]

Dad has that set. We just took bolt of the appropriate size, cut it to the appropriate length, and ground the tip to a point. Works fine. As mentioned the screw tip must be removed.

[ian maybury]

If the current set cuts well and the screw tip is easily removed that's be a good route Glenn.

Have a think Ken about what you will want to use them for - the drill in the centre won't suit if you want flat bottom or nearly so holes. One complication could be (don't know how the drill/screw is held) that if you cut back drills to suit (so that it's located on the plain shank) the drills would have to be re-ground. You could buy extra short series drills if the lengths suited. (they are available over here)

Or consider Glenn's route? It's easy to put a regular conical point accurately on a bolt or a bit of mild steel rod. Just chuck it in a power drill, and use a sharp file. (make sure it has a handle) Move the file back and forth so that a few teeth don't do all the work. Maybe the tips screw out, and could themselves be pointed. I'd test one or two before doing the lot just in case - to verify that they cut as you want.

A dab of permanent Loctite (red) thread locker might be the plan to finally secure the tip or whatever replaces them...

[Mark Wooden]

If you can't exchange them for forstners, don't grind the threads off the lead screw; instead, (if there's enough room) chuck the lead screw in your dp and file a point on the other end and use that when drilling in the dp. You can also just use some mild steel rod to make the centers. That way you still have the lead screws to use if needed.

I'm in agreement with the other as per the bits' usage- they are for rough boring in softwoods. They can be tuned a little to cut better in hardwood & ply with a file.

[ken masoumi]

Glen,that sounds like a good idea, it is easy and practical.
Ian, the large bits were originally purchased to cut thru-holes very much like a hole saw would but with cleaner edges,but if I replaced the center bit with a twist drill, I was thinking to only let the tip of the bit to stick out to mimic the brad point in a regular forstner bit .I already have a short (stubby) set I could use.

Thank you both .

[ken masoumi]

If you can't exchange them for forstners, don't grind the threads off the lead screw; instead, (if there's enough room) chuck the lead screw in your dp and file a point on the other end and use that when drilling in the dp. You can also just use some mild steel rod to make the centers. That way you still have the lead screws to use if needed.

I'm in agreement with the other as per the bits' usage- they are for rough boring in softwoods. They can be tuned a little to cut better in hardwood & ply with a file.
The bit I used actually cuts very cleanly ,no rough edges to speak of, it would have been an average set for not so critical projects.
I like the rod idea, lots of good advice so far.

[ken masoumi]

Update:
I contacted Grizzly and after exchanging 4 emails with them and after trying to explain why the 3" bit that I used from that kit could not possibly be used as is to drill a hole unless it is modified or completely removed.
The nice/friendly customer support rep contacted their tech support and finally got the following explanation:

"The product is as described being a multispur design with screw tips to pull the bit into the workpiece. However, a forstner bit is meant for drilling blind holes or holes that do not go all the way through the workpiece. The screw in the center would continue to pull the drill into the workpiece. So, if the screw is left adjusted out, it is going to pull the bit through the workpiece or it can be adjusted to the appropriate depth or be removed to work like other forstner bits. These can serve both purposes."



I thanked them for their replies and for trying to find some explanation ,although it did not make much of a difference to my problem (not being able to use it with a drill press) I still appreciated their effort.
Now I'm planning on modifying the center screw bit using one the few methods suggested here and will report back.

[John Hubbs]

Looks like you have been set straight on your bit issue. I would like to add that true forstner bits will heat up quickly if drilling too fast. As stated 500 rpm for anything over 2" is pushing it. Slow and steady.
Get a set of true forstner bits and you will find all kinds of uses for them. I would caution you, that forstner bits and hole saws will have a tendency to "punch" out the backside of wood and create some jagged edges.
Use a backer board to lesson this, or drill small pilot hole and finish cut from both sides.
Regards, John.

[ken masoumi]

Use a backer board to lesson this, or drill small pilot hole and finish cut from both sides.
Regards, John.
Excellent tip , thank you.

[Robert Willing]

I use forstner bits all the time in oak, plywood and in almost all types of woods including most exotics. I use a drill press set at about 400rpms. I bore almost thru until the nib just starts to come thru and than turn the piece over and let the small hole from the nib guide the bit thru this gives a clean hole both sides. When I make gun rack and fishing rod racks I may make as many as 60 to 80 holes for one project. I will clean up the hole with an oscillating drum sander to clean up any remaining problems.

I also make recesses holes to hold lazy Susan bearings.