Forstner bit "repair"?

Re: Forstner bit "repair"?

John C Lucas

Silver solder might be a possibility ut alignent ight be difficult

Silver solder is a good option, if

Dick Coers

You already have it. It's expensive, and this would just be an experiment. Soldering temperature will be really critical for the result and the metallurgy of the bit. With the shank in the drill press, it may keep the shank a little cooler, and having the torch raking over the brick might be interesting. Personally, I'd just pitch it.

Re: Forstner bit "repair"?

John McGaw

How wide and deep is the hole? Does the protruding stub on the head fit tightly and without wobble in the hole? Tapered or straight? Clean smooth surfaces or rough/broken? Was the bit hot when it came apart? If the stub is clean and smooth and slightly tapered, it seems as though the fit might have been something like a small Morse taper and re-fitting it would be no different that with any other of that sort.

Some pictures

JL

The shaft of the cutting portion fits neatly inside the hole in the shaft with a minimal amount of clearance.

I would have to do little or no alignment. There is a little divot in the end of the cutting portion and a little nub inside the hole in the shaft for alignment.

If it can be done cheaply, it may be worth it - as I have a torch. I would have to check my stepfather's old stash to see if I have any silver solder. I do have regular solder, but that would probably melt with the heat.

The bit is only $10.30 (plus shipping) - so I already ordered a new one.

JB Weld!?! Ha!

Re: Some pictures

john lucas

JL send it to me and I'll silver solder it. That looks like a very easy repair.

This is perfect for Red Locktite 270

Keith Newton

All you need to do is clean, put a few drops in and twist it to even the spread. It will grab within about a minute. I've bonded about 100 10mm to 1/2" bushings onto the carbide breakpoint drills to use in routers without ever having one fail. I was soldering them at first, but I've got a friend with a machine shop that guided me. You can get it at any auto parts store.

perfect for Red Locktite?

John K Jordan

There is actually something much better than Red Locktite for this type of repair - Sleeve Retainer. It is made exactly for permanently bonding two metals with a good fit. 3000 psi strength is typical.

https://www.amazon.com/s/ref=nb_sb_noss_2?url=search-alias%3Daps&field-keywords=sleeve+retainer

You can't use "regular" solder - it won't stick to steel.

It does look like an easy repair with sliver solder since the alignment should be good. The only caution is to not overheat the cutting edges of the bit if it is made from hardened steel - easy to do with a torch. Some sort of heat sync might be good. HSS shouldn't be a problem but I don't recall the temperature it will take.

I didn't know some were constructed like that. If the shaft is not hardened and there is no play you could possibly even drill a hole and drive in a roll pin.

JKJ

Re: perfect for Red Locktite?

Barry Irby

I have an original version of the Kreg Jig. Metal with hardened steel sleeves. I dogged it and one of the sleeves came out. Called Kreg and they would not fix it but they sent me a new plastic version. Someone here told me about Slip Paste (IIRC) and I got some and "glued" the sleeve back in. Its been working perfectly for about five years. I've never used the fancy plastic version. It just killed me to throw out the older version.

If the fit of the drill shaft is tight, I think the same thing would work. And I completely understand the urge to fix it, but the stuff on Amazon and probably the slip paste costs about as much as the drill bit.

Re: perfect for Red Locktite?

philip f Duffy

A few years ago a friend suggested I repair a tool rest top bar with Locktite Black. It has served me without a quiver for all these years. - -just another option Philip

Re: Forstner bit "philosophy"

William Duffield

My view of Forstner bits is to buy the cheapest Chinese sets I can find. When one breaks or dulls or overheats and loses its temper, that tells me I use that size enough to invest in a high quality German bit to replace it. I buy either Famag BorMax bits or Colt bits for heavy use. The Colt bits are especially useful for drilling deep holes because the shank is designed to lock concentrically into extensions with just a twist.

Re: Some pictures

William Duffield

That was enlightening. It explains why the big Forstner bits are relatively inexpensive, especially when you consider all the metal that would need to be machined away if you turned and machined them from one billet.

And then, I had further enlightenment tonight: I'm trying to turn a big ice scoop. I figured I could save some time and effort by doing most of the hollowing with a 3" Forstner bit. When I started to feed it into the end grain cherry, I though I saw the Forstner bit shank turn in the Jacob's super chuck. I tried again, watching more carefully for movement, and thinking about your experience. I stopped as soon as I confirmed that the head of the bit rotated relative to the shank, but at least it didn't fall out.

There was also lots of threatening noise and vibration. I decided that wasn't the right way to do the job, as I also noticed new hairline end checks in the cherry where it had heated up due to the Forstner bit friction. Maybe a sharpening job on the bit might help, but I think hollowing it the traditional way, with a bowl gouge, is going to work a lot better.

when drilling with Forstner bits

John K Jordan

...noticed new hairline end checks in the cherry where it had heated up due to the Forstner bit friction.

Something I started doing years ago which helped a lot you might want to try. I use an air nozzle and blow compressed air continuously in the hole at the back of the Forstner bit. This cools the bit and wood and keeps the chips and dust clear, which probably further reduces the heat. It does seem to cut faster. Works especially well with deep holes.

Just a thought.

JKJ

Re: when drilling with Forstner bits

Dick Coers

You must have three hands. One to crank the tailstock, one to impinge air, and one on the drill chuck to make sure it doesn't vibrate and loose the group on the morse taper. No wonder you get so much done!

Re: when drilling with Forstner bits

William Duffield

I'll give it a try, along with sharpening the bit. But, I think my JC-10 might give up before I get a 3" diameter by 3 " deep hole drilled.