Spoon bit woes

For discussion of the drilling and shaping of the stummel.
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The Smoking Yeti
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Spoon bit woes

Post by The Smoking Yeti »

A while back I got one of Pohlmann's 7/8" spoon bits second-hand-but unused. I had just acquired a metal lathe (Jet 9x20) and wanted to try out freehand drilling. My first attempt was... terrifying. The lines were lined up decently, and my pilot holes(5/32") lined up nicely. The issue came when I used the 7/8" bit to widen the 5/32" hole- a friction-ridden hot mess with me barely hanging on to the stummel for dear life.

The issues since then have only continued. I'm struggling to keep this bit drillin true in my pilot hole (I'm now drilling a 5/32" then 3/8" pilot hole in order to reduce the friction). I just finished drilling a stummel, and had the bit wander a good quarter inch farther back than my pilot hole- luckily I was drilling with my dimensions oversize so I was able to salvage it.

The other issue I'm having is extreme heat. My drill bit is generating a ton of friction, and is actually burning briar as it cuts(and my finger when I accidentally brushed it). The friction being generated is enough that at 300rpms it's binding up and stopping the bit whilst my lathe drive belt slips trying to gain enough traction to keep cutting.

What're your thoughts on my struggles? Is this a manifestation of 7/8" drilling into a small pilot hole?

Any suggestions?

Cheers!
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Tyler
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Re: Spoon bit woes

Post by Tyler »

I'd say you have a few issues. Now, I have just started drilling by hand, so take this with a grain of salt. That said, my teacher was Todd Johnson, so I feel good about what I do know about all of this.

First, you are taking a LOT of meat out in one pass. You need at least one more drill step in there. And instead of 3/8" you would benefit from a bigger second pass. I have 29/64". So, step up to a bigger second pass, then add a third before 7/8".

Second, your bit can't be sharp anymore. All that heat has likely destroyed the edge.

Sounds like you aren't using the tailstock to push the stummel onto the bit. If you do, it won't wander.

Finally, you can grind a little relief on the round of the bit behind the cutting edge; this will really reduce friction. This might not be necessary if you fix th first two issues.
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Re: Spoon bit woes

Post by The Smoking Yeti »

Well, I'm actually using the tailstock- a dull bit might be causing the wander. Are you suggesting I step up to something like 3/4" after I step up to 3/8" and before 7/8"? I'm not comfortable cutting a relief in my bit, that sounds like potential disaster for me. How do I sharpen this thing?
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Tyler
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Re: Spoon bit woes

Post by Tyler »

The Smoking Yeti wrote:Well, I'm actually using the tailstock- a dull bit might be causing the wander. Are you suggesting I step up to something like 3/4" after I step up to 3/8" and before 7/8"? I'm not comfortable cutting a relief in my bit, that sounds like potential disaster for me. How do I sharpen this thing?
If you are using the tailstock, wandering shouldn't be possible. How are you using the tailstock?

Yes, use 3/4" before 7/8".

You sharpen the same way you'd cut relief. :)
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Re: Spoon bit woes

Post by The Smoking Yeti »

What should I use to cut relief? I haz 8" bench grinder, but I'm guessing that's not the optimum tool. I'm locking down the tailstock and using the wheel to advance the stummel.
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The Smoking Yeti
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Re: Spoon bit woes

Post by The Smoking Yeti »

Also, just for clarity- you're suggesting I use a 3/4" HSS bit as a pilot, correct?
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Tyler
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Re: Spoon bit woes

Post by Tyler »

The Smoking Yeti wrote:Also, just for clarity- you're suggesting I use a 3/4" HSS bit as a pilot, correct?
How about let's switch to the phone. :D Check your PM.
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Leus
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Re: Spoon bit woes

Post by Leus »

I'm having the same issues, so please post your conclusions afterwards :-)
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PremalChheda
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Re: Spoon bit woes

Post by PremalChheda »

There is a bit of a learning curve to get it right, but I have also had the experience of the bits getting dull. I have been re-sharpening very lightly with success.
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Nate
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Re: Spoon bit woes

Post by Nate »

I drill at 400 rpm, and Brad himself told me at Vegas that he drills around that rpm as well. Everything else everyone said is worth a listen too.
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Re: Spoon bit woes

Post by The Smoking Yeti »

Tyler I swear I'll get around to calling you, I've been super swamped lately. But I need to figure this out sooner rather than later. :)
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andrew
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Re: Spoon bit woes

Post by andrew »

If the bit is "wandering" you probably did not have your lines placed correctly. It's also trickier if you are not cutting into a perpendicular surface (canted chamber). The friction? Just to make sure we're all talking apples to apples, your bit is chucked in your headstock? (not the tailstock).
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andrew
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Re: Spoon bit woes

Post by andrew »

Grinding relief into the back of a spoon bit is a little tricky and should not be necessary unless you are hogging a lot of material. I use a 3/8 bit for my pilot and that helps. Is your bit hardened?
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sethile
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Re: Spoon bit woes

Post by sethile »

I find spoon bits will wonder off a very undersized pilot hole at the top regardless of what's going on with the tail stock. Adding the extra steps up in pilot bit diameter before going to the spoon bit will help a bunch. Modified Silver and Deming bits work great for this. I'd love to know how you folks are modifying them. I have some that just happened to work well (don't grab much). But even those wonder a little at the very top of the hole if I'm not extra careful with holding the stummel.

My experience is that Brad's last bits (his 2nd generation) cut about a million times better than his first, which really do need some sort of relief, and/or very regular sharpening to cut cleanly for me.

And finally, this also takes practice and a bit of playing around with the process based on your tools to get the hang of it.
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ToddJohnson
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Re: Spoon bit woes

Post by ToddJohnson »

My Process:

1. Drill with 3/16" bit until you intersect the airway.
2. Drill with modified 29/64" bit with a V-shaped profile so that it does not grab the pipe and suck it on to the 3/16" pilot. Getting the "proper" profile on this second pilot bit is a bit of an art, and the only thing I know to tell you is that it involves trial and error. It should track with the 3/16" pilot, but it should require a significant amount of pressure to go down. If it grabs, it's too sharp. If it burns it's too dull. Mine is 12 years old and I don't mess with it. I've made a handful of others for guys over the years and I still don't know what the "secret" is. All I know to say is that it's "right" when it works.
3. From here, I go directly to the spoon bit. The key with the second pilot (in my case 29/64") is that it must be slightly larger than the "tip" of the spoon bit, and smaller than the largest diameter of the spoon bit. That is really the only way the spoon bit will "track" correctly with the pilot bit. I start with the tailstock, and I do not use the quill, I push the tailstock onto the spinning spoon bit for the first half of the drilling. Then I abandon the tailstock and finish by hand. If I want to enlarge the chamber, I move up to the next largest spoon bit using the tailstock to keep the alignment. Rinse and repeat if you want to enlarge it further.

NOTE: If you're using a "bull nosed" spoon bit, you're really at a disadvantage. Mine are all continuously tapered, and if they're not you will generate so much friction that you're burning the wood and it's nearly impossible to get a "clean" cut. The other problem with this is that you have to have a much larger (second) pilot bit because there is no difference, really, between the diameter at the "tip" of the spoon bit, and its full diameter.

Other notes: I drill at 550 RPM's and if you're using a small or cheap lathe, it is likely that, in order to move along the ways, your tailstock is either too loose or too light, and you will get a bunch of rattling. There are some modifications you can do to the "through bolt" at the base of the tailstock that will rectify this. I think if you search Google for "mini-lathe tailstock modifications," you can find several "fixes" for this problem. My tailstock probably weighs about 60lbs., so it never rattles and moves around, but again, if you're using a 9" x 20" which I would consider both a "small" and a "cheap" lathe, then much of your difficulty probably has to do with your tailstock.



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The Smoking Yeti
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Re: Spoon bit woes

Post by The Smoking Yeti »

So I've got it cutting much nicer, my final pilot bit isn't well balanced though. Since I'm using a 7/8" spoon bit, the final pilot is a nice even 3/4". Drilling is going smoothly most of the way into the chamber, until the last bit. In the last 3/8" down there is still quite a bit of material to take off, so there's a lot more friction. I'm having some difficulty here, but I think I can eliminate most of them by playing with the depths of my step drills. Methinks it'd all be easier if I just had a 3/4" spoon bit.

Thanks for the info Todd! I'm gonna get artsy with my 3/4" pilot. I'll let you know how it goes.
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