Drilling Ash, much smoke, sage advice anyone?

[J. Clarke]

7/8 Forstner, in drill press at lowest speed (350 RPM). Carbon steel. Bit sharp (how do I know? Worked it over with a fine grit diamond file las time I used it. This time I managed to slice myself taking it out of the box--it didn't hurt until I saw the blood).

By the time it's maybe a quarter inch into the ash, much smoke. Tried a piece of poplar and a piece of Douglas Fir, no smoke. Shavings coming out are fine, continuous, hole is clean other than looking burned. Continue on--cut a quarter inch, pull the bit out, repeat. By the time I'm 3 inches in the bit is hot enough to burn me, overall yellow (not just the edge, all the way up to the shank--not yellow-hot but the straw-yellow discoloration you get when drawing the temper).

Does the same thing on the lathe at lowest RPM (500).

Drilled a dozen pieces 3 inches deep, drill continues to cut fine, so am assuming that yellow is something coming out of the Ash and not indicative of the bit losing temper.

Now, obvious thing to do is get a carbide bit for this job (it's going to be continuing I hope). But was wondering if anybody had any other sage advice.

[Morgans]

"J. Clarke" wrote

Could be you got it too hot before you sharpened it, and it lost its temper.

Though I would remind you that the larger the bit, the slower the speed is required. 250 RPM might be slow enough to do the job.

[woodstuff]

I can sharpen pretty well, but I am thinking of the times when things didn't get as sharp as I thought they were and were just dull enough to make a difference. The sharpenss or dullness can usually be experimentally determined by the volume of blood a cut on your finger produces :-)

[mac davis]

I'd have to say it's a resin or something in the ash, since everything else you drilled was ok..

mac

Please remove splinters before emailing

[Lew Hodgett]

------------------------------------- SFWIW.

Recently completed an intro wood working course at a local community college.

Was taught to feed a forstner bit as fast as possible to avoid burning.

Lew

[Larry W]

I've read that too. And perhaps worth trying, use a HIGHER speed. Various drill speed charts I've seen for forstners recommend something around

1200 or 1500 RPM for a 7/8" bit in hardwood. I know that that is contrary to a lot of the previous advice, but my old Delta radial has a minimum speed of 650 IIRC and I've used it plenty of times with forstners up to 1.5 inches or so. And pull the bit out more frequently than every 1/4". Only leave it in contact with the wood a few seconds at a time.

[J. Clarke]

This particular bit is clearly marked "Max 870 RPM".

If you know of such a chart online I'd like to see it. All the generics I find say 500 RPM for hardwood.

[Morgans]

"J. Clarke" wrote

I still think that the bit has lost temper, if it was getting as hot as straw temperature, as you were saying. Straw temp is for making steel soft. Bad for bits. You now must get the bit up a bit hotter than straw and oil quench it to get hardness back.

Another question, about how you sharpened it. I hope this is not insulting, but I have seen bits sharpened very wrong, before.

The leading edge angle of the cutting edge is critical. If you sharpen the leading edge, it must be sharpened all of the way up the face, to maintain the angle of the leading edge of the cutting surface. The angle of the bit behind the cutting edge is critical, too. If it does not go upwards rapidly enough, the bit will not be allowed to cut as thick of a chip as necessary to cut without burning. The chips coming out of the cut should be thick, and long, not too unlike a sharp bit cutting steel. It will not be a curly-cue as steel would be, of course, but the chips should be much thicker than dust from a circular saw. Even if it is not sharpened correctly, it will still cut fairly well in softer woods.

[J. Clarke]

I'd be inclined to agree with you if it wasn't yellow all the way up the shank. I'd expect some blue somewhere around the edge if it got hot enough to go yellow all the way up, but there's no blue on it.

Assuming it's an oil-hardening steel.

Yep. Diamond file places in contact with full face and full face sharpened. Sharpening Forstners is easy. And it cuts fine in everything but ash.

What comes out of it is the same quality of chip that I get from a block plane.

[krw]

Nope. I have a boat-load of Ash (probably 300bf left of 600) and have never had that problem with drill bits. Sometimes I'll see a burn mark from a saw blade but never smoking drills. It is hard stuff, though.

[Morgans]

"J. Clarke" wrote

That sounds great.

Yet it burns? Strange.

Where on the hole is it burning? The sides, or the bottom of the hole? If it is the bottom of the hole, and it is a through hole, don't worry about it. (easy to say) If it isn't a through hole, then put some stain on the burn and go with it.

I think the only thing left to try is slower speed. From machining philosophy, if it is too hot, slow the tool speed, or cool the workpiece and bit. Since cooling them is impossible, that remains slowing the tool.

How about increasing the relief angle on the bit. Making it steeper? How about letting the bit be cooled by drilling and waiting, and so forth? How about blowing a stream of high volume, high pressure air onto the bit to help keep it cool?

It seems like you have everyone baffled. You need to experiment, figure it out, and come and tell us the results, me thinks.

[Morgans]

"J. Clarke" wrote

Wow, I just realized how deep you are drilling. Drilling that deep in hard stuff would be bound to heat the bit.

Try a closely directed stream of compressed air on the bit. Cool that sucker with air, and slow down the drilling process if the burning is objectionable.

[J. Clarke]

Good question. It appears to be the sides. The bottom is pretty much the same color as the rest of the piece.

And the drill press is on its lowest speed now, so without reworking it somehow that's out.

That's a possibility.

When I gotta do 70 of these at a time without an NC machine that's not all that workable.

Another good possibility.

I think I'm just going to say to Hell with it and spend the 25 bucks for a carbide bit.

[Lew Hodgett]

--------------------------------- Trying to clear chips from a forstner bit in a 3" hole can be a problem.

Think I'd use a brad point drill for this operation.

Lew

[krw]

The fact that it's burning on the sides indicates to me that the side of the bit is rubbing on the wood, like there is excessive runout on your drill or bit.

If the problem is the bit, that should solve it.

[Morgans]

wrote

Runout could be the problem, but I think it is more likely that the burning is because the outer teeth have lost their "set."

When this type of bit is new, (for new woodworkers in the group) the row of small teeth around the outside are slightly further out than the main diameter of the bit. When they wear and get sharpened, the outer point is what wears down. The only way to fix a bit like that is to knock the teeth back out a little, or reduce the diameter of the sides of the bit a bit.

[J. Clarke]

This is a classic Forstner--no teeth.

[Morgans]

"J. Clarke" wrote

Now it all makes sense.

I have always liked the type with teeth. Faster cutting, easier to turn, and clean holes.

I would bet you could use one of those with teeth, and it would do just fine, without having to go to an expensive carbide model.

That has been my experience, anyway. I have a couple sets with teeth. I have one (1 1/8th, I think) without teeth. It usually goes unused.

[J. Clarke]

Have to give one a try.

[whit3rd]

There's one other possibility: if there is a buildup of sap on the bit, a bit of cleaning (brass wire brush or chemical) can remove the material that is rubbing and causing the heat.