Tool rest height for scrapers..........

[odie]

It's my opinion that, for bowl turning, the tool rest height for scrapers is less forgiving than that of gouges. Basically, this is because the gouge needs to have a rubbing bevel, and since the bevel angle can vary to a great degree, the tool rest height can vary considerably according to the physical stature of the turner.

Since I'm 5'9", and generally keep my scrapers fairly level, my findings are based on that, but shorter or taller turners may have to adjust accordingly........regardless, the scraper's cutting edge should always point directly toward the center of the turning.

It's my opinion that the cleanest cut is when the scraper's cutting edge is at the centerline of the turning. This holds true, whether the scraper is used in a traditional fashion, or is tilted for a shear scraping mode. Either way, the best quality of cut is when the wood is moving straight down.

The tool rest height, in order to maintain the best scraping cut, is dependent on the distance between the top of the tool rest and the height above it the cutting edge of the scraper meets the wood. The two main factors that make this height a variable, is the scraper thickness when used traditionally, and the scraper width in the case of shear scraping.

The best way I've found to nail the tool rest height adjustment, is to use a block of wood that shows exactly where the centerline of the lathe is. (see photo) With the scraper on the tool rest, and pointed at the height block, it's easy to see if it's a match, or not......adjust accordingly.

(On the bowl exterior)
If the scraper goes above the centerline, it can be a dangerous situation because the wood is now moving TOWARDS the cutting edge, and can have a severe catch. If the scraper is presented to the wood below the centerline, it's safer because the wood is now moving AWAY from the cutting edge.......but, the further below the centerline you go, the worse the quality of cut will be.

(On the bowl interior), all of the above is the exact opposite......safer to go above centerline, but dangerous to go below......and best cut is normally at centerline. There are times when it's advisable to go well above centerline, strictly for safety reasons. There doesn't seem to be any hard-fast rules about this, because each bowl shape, species, thickness, rpm, etc., can, and does effect what works best.

The only hard-fast rules that are universal seems to be avoiding cutting above center on the outside, or below center on the inside.

Anyone who agrees, disagrees, or has any other comment, idea, recommendations, whatever.......is welcome to contribute to this thread.

ooc




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[john lucas]

I just adjust my tool rest close and then move my body to achieve the slightly downward tilt of the scraper. I do everything with my body as much as possible and not my hands. You have much more control that way. I never really worry much about how high the tool rest actually is in relation to the bowl. It's just a fulcrum point. What I want is the tool cutting at the proper place on the bowl and the handle is on my body where it's most comfortable. The tool rest is positioned to give me these two results and may be well above or well below center depending on which tool I'm using and how I use it.

 

[Charles Henderson]

I would add that a general tool rest height for scraping is a bad idea unless all of your scrapers are the same thickness. For instance, I have a thin scraping tool (mostly for shear scraping) that will usually but the rest just a hair above center. I also have an heavy duty scraper (9/16 thick) that will put the rest about a half inch below center. With that tool, If I go very far over the rest, I'll raise it a little bit more to get a better downward angle toward center.

Additionally, I personally prefer to shear scrape only if I can. I've had some catastrophic catches just by catching too much of the cutting edge inside of a form. When shear scraping you have much more control of how aggressively you wish to cut. It is my opinion that you can get just as deep a cut, and a much lighter cut while shear scraping as you can with the scraper flat. The cut will also leave much less tear out to deal with, and if you happen to catch, then you just might have time to react before the entire tool contacts the rest and causes a catch.

Oh, scrapers rule to all of you gouge snobs

 

[odie]

I agree with the cutting positions. For additional info there are video clips at Robert Sorby under their "Multi Tipped Hollowing Tool" which also has a scraper.

For center height for the tool rest, I adjusted mine to a drive spur center and marked it. A light pass around (1/64 inch or less deep) with a hack saw scored it enough to paint in the gold line. On a one inch post this would never compromise the integrity of the post strength.

I also use small hose clamps with a large thumb screw to set the post height (to any position) instead of a collar with a set screw. These are available at AutoZone for about two for 3 dollars.

Mike

Hi Mike.......

Thanks for letting me know about the thumb screw hose clamps. That sounds like something I would like to add to my tool rests......

I'm putting it on my list of things to get!

OOC

 

[odie]

Hi Mike again......!

I don't have an Auto Zone in my area, so I checked around and found those thumb screw hose clamps at Ace Hardware.........thanks again, I've been needing some of those! :cool2:.....very :cool2:!

They were $4.49 for a pack of two.......I got four!

OOC

 

[odie]

I would add that a general tool rest height for scraping is a bad idea unless all of your scrapers are the same thickness. For instance, I have a thin scraping tool (mostly for shear scraping) that will usually but the rest just a hair above center. I also have an heavy duty scraper (9/16 thick) that will put the rest about a half inch below center. With that tool, If I go very far over the rest, I'll raise it a little bit more to get a better downward angle toward center.

Additionally, I personally prefer to shear scrape only if I can. I've had some catastrophic catches just by catching too much of the cutting edge inside of a form. When shear scraping you have much more control of how aggressively you wish to cut. It is my opinion that you can get just as deep a cut, and a much lighter cut while shear scraping as you can with the scraper flat. The cut will also leave much less tear out to deal with, and if you happen to catch, then you just might have time to react before the entire tool contacts the rest and causes a catch.

Oh, scrapers rule to all of you gouge snobs

Charles.......

Just a note of confirmation that you are absolutely right about not using a general height setting for all scrapers. As you said.......this is because all scrapers aren't the same thickness.

An exact scraper height that is temporarily "fixed" for one thickness of scraper is useful to me. This is because, in the course of using a particular scraper, I often find the need to revolve the tool rest post within the banjo to continue what I'm working on........this is where the value of the quick adjustable, but temporary height settings that the thumb screw hose clamps allow, really shine! I can swivel the tool rest without losing the exact height setting I was using! :cool2:

This is something I've been needing for some time now. Glad you came on and solved this for me! :cool2:

PS: I also agree about the "gouge snobs"! Scrapers have been putting a very refined cut to spinning wood for ......oh, probably centuries! Some turners seem to think using scrapers for a finish cut is showing lack of experience.....but, I'm going to have to disagree with that notion. Personally, I feel there is a skill level that very few turners achieve.....with scrapers. That's because they are "conditioned" to think a scraper is just for beginners. (This is not to encourage any thought that gouges don't require a great degree of skill, as well.)

OOC

 

[odie]

Hi Mike again......!

I don't have an Auto Zone in my area, so I checked around and found those thumb screw hose clamps at Ace Hardware.........thanks again, I've been needing some of those! :cool2:.....very :cool2:!

They were $4.49 for a pack of two.......I got four!

OOC

Just a note.......those plastic turn knobs will work loose from use. They were intended to be a convenience for the end user, then removed after the hose clamp is set. Since our purpose is for lathe use, the plastic knobs are in constant use. I epoxied mine on permanently a few days ago.

ooc

 

[Dave Ogren]

Scraper Tool Height

I am pretty new to wood turning (84 Bowls since April this year) I have a couple of scrapers and had read that sooner or later a person will get a giant catch, so I didn't use them. Then I read in a forum about tucking the handle under your arm pit, raising the tool rest high enough to then place the cutting edge at about center. That made sense to me and I started using that method to finish turning my bowls about 25 or 30 ago.
I think that it works well, but I am new to this.
Some stats, are I am 6'1 1/2" tall and my spindle height is just above 49" tall. Please correct if I am missing something.
Thanks again for your wonderful forum and all of the advice.

Dave

 

[odie]

I am pretty new to wood turning (84 Bowls since April this year) I have a couple of scrapers and had read that sooner or later a person will get a giant catch, so I didn't use them. Then I read in a forum about tucking the handle under your arm pit, raising the tool rest high enough to then place the cutting edge at about center. That made sense to me and I started using that method to finish turning my bowls about 25 or 30 ago.
I think that it works well, but I am new to this.
Some stats, are I am 6'1 1/2" tall and my spindle height is just above 49" tall. Please correct if I am missing something.
Thanks again for your wonderful forum and all of the advice.

Dave

84 bowls since April......for me, that would be a grueling pace! My average is probably about 50 per year, or about 1 per week. Good for you......you are gaining knowledge quickly.

I'm 5'9", but I have shrunk some in my old age! Last time at the Doctor's office, they tell me I'm not quite 5'8", but I suppose it's my ego that still makes me claim my military height of 5'9"!......I'm 60yrs old.

To tell you the truth, I don't even know the spindle height of my Woodfast. I'm heading out to the shop right now to find out for sure. In any event, whatever the height is, is what I've gotten used to.....and feel comfortable with.

This will be the same for you.....I don't believe any hard fast rules will apply to you. You are an individual, and your body will let you know if you're stooping too much......or wish you were taller to accomplish that certain task. Longer, shorter arms, spine, overall height......it would be hard to come up with a formula that works for everyone.

brb

My spindle height to the center is 43 1/2".

ooc

 

[Dave Ogren]

Thank you ,Odie

Dave

 

[odie]

Thank you ,Odie

Dave

You are certainly welcome, Dave.....

ooc