Need Help With A Problem Parting

[Dom Garafalo]

I'm a new turner and have been watching you tube videos on wood turning and working to develop skills sharpening and using my tools on primarily spindles and some basic shaping on small bowls. I also joined a local wood turners club.

I have been working mostly with lamented pieces of cherry and poplar and have been making progress but have been struggling with getting consistent results with my parting tool which is one that was part of a harbor freight set. It has 25-30 degree bevel angles forming the point which is sharp and square to its sides.

I've been using a plunging cut which seems to work better for me than a straight in cut and it works great with small diameter spindles up to about 2 inches and it seems to work especially well with cherry.

Where I'm having a problem is when the diameter increases. For example, I've been experimenting shaping small bowls about 2" x 6". I am attaching the bowl blanks to glue blocks that are about 3" OD with CA glue and then mounting the glue block in my chuck and turning it which has been working great. The problem surfaces when I try parting off the bowl at the glue line.

I experience some initial cutting followed by a lot of squealing with less cutting action. I've tried raising and lowering the rpm's and the height of the tool rest but nothing seems to help. I've widened the parting cut to eliminate friction and I've even stopped to re-sharpened the parting tool which made a small difference but the tool is just not cutting very well in this particular situation.

Based on what I've said, is there something obvious I'm doing wrong, not doing correctly or at all, creating my own problem by using lamented pieces of wood, etc? What does the squealing indicate?

I would appreciate your thoughts, comments and suggestions.

Thank you

[Allan Ferguson]

Just pop it off with a chisel and mallet.

[Edward Weingarden]

As Allan said. Tap a chisel at the glue joint. Then reverse mount the bowl to finish turn the bottom.

[Brice Rogers]

If you can't pop it off and want to part it, here is what I'd recommend:

1. Start with a peel cut (see Youtube videos) where you are perhaps holding the tool pointed upwards, first scraping the bevel (no cut) and the pulling back and lower the tool handle until it cuts. You will be cutting above center until you get real close to center where you'll let the cutting edge go into an arc capturing the center. Go in perhaps 1/2 inch and then remove the tool and re-insert it to make the slot about 50% wider. The reason why you are getting squeeling is probably it is getting pinched and some glue issues (see #3).
2. About every half inch, widen the cut again
3. The glue that you used for laminating may be something like Tite-bond and may be less than rock hard. The CA glue will get a bit gooey if it gets hot. With a plunge cut, you may be getting some vibration/chatter. Get the tool rest as close to the piece as possible. Doing parting often leads to a lot of "overhang". I've read that no more than 20% of your tool should be hanging out there. I don't recall that the HF tools were particularly long.
4. I sometimes will use a parting tool to start the separation and will finish up with a hack saw if I have too much overhang.
5. When you are gluing your part to the waste block, make sure that you leave a concave recess in either your bowl or the waste block or both. The only portions that should be in contact and glued are perhaps 3/4" on the size bowls you are doing. Most of the holding power comes from the outer portion, so if the center is not glued, it doesn't matter much for strength. But when you're parting, once you reach the recess, it'll let go.
6. If you are still having problems, try cutting on either side of the glue line (either into the waste block or the bowl side) and avoid trying to cut the glue - - see if it helps.

[John Keeton]

For what it may be worth, I finish and embellish the base of all my turnings, so I don't part of the waste block. When I reverse a piece, I use the center mark for tailstock support. With a small bowl gouge, I peel away all but a small "post" of the waste block and detail the bottom. For that reason, I want my waste block and base in full contact and glue on the full joint.

[Len Mullin]

Dom, try parting it off just ahead of the glue line, don't part it right on the line. The wood is softer than the glue, so you'll get a smoother cut.
Len

[robert baccus]

A 3" dia. glueblock is probably overkill for a piece that lite. Try backing off to a 2" GB and it should pop off.

[Dom Garafalo]

When you are gluing your part to the waste block, make sure that you leave a concave recess in either your bowl or the waste block or both

I have been doing this leaving about a 1/2" gluing surface on the outside of the glue block.

A 3" dia. glueblock is probably overkill for a piece that lite. Try backing off to a 2" GB and it should pop off

I will definitely try this next. Is there a formula or guideline for sizing the glue block to the bowl diameter?


One thing that is never mentioned in all the videos or descriptions on parting is the recommended spindle rpm. Is there one?


Thanks everyone for your comments and suggestions. I will try the things you all mentioned to see if I can improve my parting technique.

[Reed Gray]

Well, if you want to use a chisel to pop it off, you need a paper glue joint. So brown grocery bag paper glued onto waste block, then block glued onto the paper. That provides a good hold, but the chisel will easily separate the joint. Other than that, learning the peeling cut really helps for a smoother cut when compared to holding the handle level and plunging straight in. Thin parting tools like to wander as you go in, but standard for me is about 1 1/2 to 2 times the thickness of the tool.

robo hippy

[Dom Garafalo]

If you use a piece of brown grocery bag glued onto a waste block then to a turning block, would you use one of the titebond wood glues?

Can someone comment on whether there is a recommended spindle speed (rpm) for parting wood when you want to separate pieces.

Thanks for the helpful information

[Reed Gray]

Rule of thumb for waste blocks for bowls, I would guess is similar to tenon for a bowl, about 1/3 the diameter. So, for a 12 inch bowl, 4 inches is VERY secure. You can get away with 3 inches, but you have to hollow out with less pressure, and one catch can shear it off. Two inches, just about impossible.

Speed range is highly variable for turning. There are a number of formulas out there, but I never had a lathe with any kind of read out on it. Smaller spindles like pens are frequently over 3,000. I would turn a 12 inch bowl, when it is trued up and balanced, at 2200 rpm, which is the high end of my middle speed range on my lathe. That is way faster than most other turners go, but not as fast as Jimmy Clewes.... A must see demonstrator. 500 is pretty slow, 1000 if it is balanced is fine. As much as anything, start slow and ease the speed up as you get more comfortable. When the speed goes up, accidents are way more spectacular...

robo hippy