The subtleties of tool rest height?

[Jamie Straw]

Trying to get an organized picture of which situations lean toward a dead-center tool rest, or others to a slightly raised tool rest. I adjust it occasionally by feel, but would like to have some insight. Thanks.

 

[Hy Tran]

Trying to get an organized picture of which situations lean toward a dead-center tool rest, or others to a slightly raised tool rest. I adjust it occasionally by feel, but would like to have some insight. Thanks.

When using a gouge (rather than a skew or scraper), you generally want the edge of your tool to be on the centerline. If you're using a bowl gouge with the bevel (rather than with the wing to scrape), you will generally want to have the tool itself be level. Therefore, your tool rest would be just a bit below centerline.

If you take this to its logical conclusion: If you're using the theoretical 3" bowl gouge (as in 3" diameter shanks , because the tool is so large, your tool rest would be lower than if you're using the 3/32" bowl gouge. In both cases, your tool edge is at centerline where it meets the wood.

When using a scraper, you generally want the edge of the tool to be on the centerline, so again, your tool rest is a bit below centerline.

When I use my skew as a skew, rather than a scraper :-O, the tool edge meets the wood well above centerline--maybe around the 10 o'clock or 10:30 position?

This is all theory, of course--in practice, there's a bit of leeway with respect to centerline, level, etc.

The geometry of a catch is something at which I'm a practical expert

 

[hockenbery]

Tool rest height depends a lot on how you hold the tools.
For bowls A scrapers flat on the tool rest, the tool rest should be set so the scraper held level is a bit below center on the outside and bit above center on the inside.

Gouges - I set the tool rest so that the nose of the gouge is cutting at center when the gouge is level.
When I shear scrape or pull cut I drop the handle and the tool works way above center and I keep the tool rest as set as above most of the time.
Once in a while I will have shape where I need to drop the tool rest height a bit lower to get the bevel to ride on the pull cut.
Basically setting the tool rest so the gouge cuts at center with the tool level is good place to be.

A low tool rest can let the wood drive onto the gouge-definition of a catch.
Don't let the wood drive onto the tool and you'll never have a catch.


For most spindle work I like the tool rest a bit higher than center so I can work on the top of the spindle.
For thin spindles I like to cut on the side toward me with my fingers behind the spindle so I lower the tool rest so I can cut on the front center.

 

[robo hippy]

I never worry about 'perfect' height, mostly because it isn't critical, and I can adjust without thinking about it. When I took a 3 day workshop with Stuart and Allen Batty, Stuart would come by and adjust my tool rest for me. Since I tend to hold my gouges level when cutting, I prefer the rest to be pretty close to center height. Easy to angle the handle up or down a little so I can be cutting closer to the center line. When cutting with dropped handles, it can be a bit lower than center with no problems. With scrapers, since you always want them angled down a bit, I tend to have it close to center height on the outside, and a bit above center when turning the inside. This aids what Al already commented on as to how scrapers should cut a little below center on the outside, and a bit above center on the inside.

Now, I know all about stop collars on the tool rest posts. Small pieces of PVC or end grain hollowed out pieces that keep the tool rest at the perfect height. I do keep one on my McNaughton tool post, but other than that, it seems that I move them around and up and down a lot. I do like the idea of what Lyle Jamieson does with his tool rests where he has a threaded post and a big nut on it for adjusting height. Simple to raise or lower a little bit.

robo hippy

 

[Jamie Straw]

I never worry about 'perfect' height, mostly because it isn't critical, and I can adjust without thinking about it. When I took a 3 day workshop with Stuart and Allen Batty, Stuart would come by and adjust my tool rest for me. Since I tend to hold my gouges level when cutting, I prefer the rest to be pretty close to center height. Easy to angle the handle up or down a little so I can be cutting closer to the center line. When cutting with dropped handles, it can be a bit lower than center with no problems. With scrapers, since you always want them angled down a bit, I tend to have it close to center height on the outside, and a bit above center when turning the inside. This aids what Al already commented on as to how scrapers should cut a little below center on the outside, and a bit above center on the inside.

Now, I know all about stop collars on the tool rest posts. Small pieces of PVC or end grain hollowed out pieces that keep the tool rest at the perfect height. I do keep one on my McNaughton tool post, but other than that, it seems that I move them around and up and down a lot. I do like the idea of what Lyle Jamieson does with his tool rests where he has a threaded post and a big nut on it for adjusting height. Simple to raise or lower a little bit.

robo hippy

Not looking for "perfect" just wanting to understand the generalities, and this thread has been a big help. Envy you your workshop with the Batty's, I really enjoy the elder's video(s). Interesting approach, Jamieson, clever!

 

[Dean Center]

Proper tool rest height is such that the distance between the top of the banjo post and the the bottom of the tool rest is very slightly more than the knuckle on my index finger. Shall I bring my index finger to you, or do you want to mail me your banjo and tool rest?

 

[john lucas]

It depends a lot on two things. Where you like to hold the tool on the wood for a certain cut, and where you like to hold the tool handle, either against your body like I do, or some other way. You take these two points and then just move the tool rest up until it touches the tool.
The others have covered the generalities. I do a lot of pull cuts with the tool handle quite low and cut with the wings of the tool. For this cut I like to be cutting at or above center (I'm talking bowls and hollow vessels not spindles). The lower the tool handle the more you create a shear cut. This means a very low tool rest position. If you have a very low tool handle it also lets the bevel of the wing on a bowl gouge become a very long bevel and virtually eliminates catches. If you think about the wood coming down almost parallel to the cut edge you can better understand what I'm talking about. Usually the edge is less than parallel but I hope that's a good way to describe how the bevel of the wing works in a pull cut.
For most push cuts done with bowl or spindle gouges I like the cut to be just a little above center, and the tool handle is on my hip. this usually leaves the tool rest around the center. sometimes below, sometimes above. It's where the tool s cutting that's most important not exactly where the tool rest is.
For Scrapers you should be above center so the tool rest will be at least on center but again that depends on how tall you are, how tall the lathe is, and how you hold the tool. Lets assume for a second that you are short and the lathe is tall and your turning a spindle. You could actually be cutting at say 8 oclock, which we would call below center and then the tool rest would be even lower. However if the cut is perpendicular to the center of the work it will act just like if you were taller and the tool was parallel to the floor with the tool rest on center. The wood doesn't know where you are, it only know the angle the tool is attacking it. I hope that didn't confuse the heck out of everybody It's one of those things that easy to show but very hard to describe. Things are different when turning the inside of bowl because you can't angle the tool rest to cut above or below center. In that case you are more limited. I often demo on lathes that are much taller than mine and consequently will have the tool rest quite low from the center line parallel to the floor. However the tool is usually roughly perpendicular to the center line of the piece so my cuts are safe and where they should be.
for turning beads on platters using a spindle or detail gouge I move the tool rest far above center. This allows me to turn the bead using the same motion I do when turning beads on a spindle, by rolling the tool. I often demonstrate this while discussing tool rest height. I will put a steel bar into the banjo and it points straight up. Then put my tool against it and turn a bead on a platter where it looks like I'm cutting at 1 oclock. That's part of how I describe that the wood only know how it's being attacked, not where on the clock it's actually doing the cutting.
For the most part everything everyone else has said is a very good starting point. Just don't get hung up on the tool rest height having to be exactly at a certain point. Be more concerned with where and how the tools is cutting and then adjust the tool rest so it's comfortable for you.

 

[Jamie Straw]

Not looking for "perfect"...

It depends a lot on two things. [snip] Be more concerned with where and how the tools is cutting and then adjust the tool rest so it's comfortable for you.

John, thanks for the (as usual) detailed and thoughtful response! It addresses directly the OP "Trying to get an organized picture of which situations lean toward a dead-center tool rest, or others to a slightly raised tool rest." Didn't want folks to think I was looking for a measurement complete to 2 decimal points. Everyone's been helpful with their practical advice on this.

 

[john lucas]

I guess early on I read somewhere that you should put a band clamp on your tool post so the tool rest would stay at the same center height all the time. I did that for a while because that's what the "books" said. Well many many years later after trying all kinds of cuts and tools and different techniques I found myself constantly changing the height of the tool rest. So I did away with that idea and started trying to understand why I move the tool rest. Some day I plan to do a video on just that but since I'm still without a shop for at least another 6 weeks or so it will have to wait.

 

[Jamie Straw]

Proper tool rest height is such that the distance between the top of the banjo post and the the bottom of the tool rest is very slightly more than the knuckle on my index finger. Shall I bring my index finger to you, or do you want to mail me your banjo and tool rest?

How 'bout if I mail you my index finger and new tool rest, and you place a fine mark at the "perfect" place on the post?

 

[Dean Center]

How 'bout if I mail you my index finger and new tool rest, and you place a fine mark at the "perfect" place on the post?

I'm afraid that won't work. It's highly unlikely that you have a standard finger.

Seriously, you have received excellent responses to your question and all I have to add is that I find myself adjusting the height from time to time when things inexplicably don't feel right. "1.25 standard left index finger joints" is intended to suggest that there is not a precise, simple answer, as you have wisely stated.

 

[Jamie Straw]

It'll be a good video topic...

[snip] So I did away with that idea and started trying to understand why I move the tool rest. Some day I plan to do a video on just that but since I'm still without a shop for at least another 6 weeks or so it will have to wait.

Very glad to hear that video is on your list! I'm sure it will be very helpful to us newbies and novices. Happy waiting on the shop, that's gotta be tough.