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Forum topic by socrbent posted 03-07-2015 02:44 AM 945 views 0 times favorited 11 replies Add to Favorites Watch
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socrbent

419 posts in 1737 days


03-07-2015 02:44 AM

Topic tags/keywords: question ash lathe turning

Maybe a better question is should I try to save it? I roughed out 2 bowls from ash this summer and left them in paper bags to dry. When final turning the first one, as I was cleaning up the outside after bringing both inside and outside back to round and getting inside to the point of sanding, I got a catch that blew it up and broke the bowl into 1/3, 2/3 at 2000 rpm.

firewood

Despite some pretty violent shaking the big part mounted by a mortise stayed on the jaws.

mortise in bowl bottom


Nova chuck with jaws

No injury or damage to lathe but it was a real scare.

After waiting a week to settle my nerves, I mounted the other bowl and brought its outside back to round. As I was bringing the inside back to round with a freshly sharpened round nose scraper, it caught and broke the mounting tenon at 1200 rpm.

Tenon


Catch

What remains of the tenon does not look usable IMHO. Should I use cole jaws to reverse mount the bowl. flatten bottom and glue on a new tenon and proceed or throw it away? I have a pretty deep gouge from when I turned the bowl green that must be resolved.

inside gouge near rim

What is your advise?

-- socrbent Ohio


11 replies so far

View LeeMills's profile

LeeMills

273 posts in 768 days


#1 posted 03-07-2015 03:32 AM

IMHO the first bowl is not able to be salvaged.
The second bowl MAY be saved but.
First, how long is that tenon/spigot? It can not hit the base of the jaws; the top of the jaws should fit firmly against the wood.
Second, I assume those are the 50mm jaws. You DO NOT cut a dovetail for those jaws. If you look at the instructions (under forming the spigot) notice the last line, typically all in capital letters. You cut the tenon/spigot straight and allow the jaws to bite in.
Third, I seldom use a scraper in a bowl but I am told it is very easy to get a catch, especially when you get out near the rim. Maybe others have more first hand experience.
Here is a link to some videos by Stuart Batty. He has three very good ones on chucks, tenons/spigots, and recesses. I have some pics I can post but his videos are very through and 10-15 minutes each.
https://vimeo.com/woodturning/videos/sort:alphabetical/format:thumbnail

Good luck on returning it and be safe. It may be difficult to re-true the tenon and have it large enough. Depending on the thickness you may be able to remove it and cut a recess instead; 1/4” deep should be plenty for the recess.

-- We cannot solve our problems with the same thinking we used when we created them. Albert Einstein

View BurlyBob's profile

BurlyBob

3695 posts in 1733 days


#2 posted 03-07-2015 03:45 AM

Man, Sure am glad your not hurt! That would have left a bruise! Those are the very reason I don’t much care for turning and lathes. I’ll stick to flat lumber. Good luck in the future.

View LeeMills's profile

LeeMills

273 posts in 768 days


#3 posted 03-07-2015 03:58 AM

Oh, and the speed. I don’t know the diameter but here is a chart from Teknatool (Nova) on recommedations for their lathe.

For your unbalanced (rough) I would stay with 700 or less.
A general rule of thumb is Diameter X RPM = 6,000-9,000. I just shorten it to “about 7,500”.

-- We cannot solve our problems with the same thinking we used when we created them. Albert Einstein

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socrbent

419 posts in 1737 days


#4 posted 03-07-2015 02:46 PM

Lee – Thanks for the suggestions. I do have a lot to learn. I kept the speed low on both bowls until they were balanced. by the chart, 2000 was 2 high on the first bowl whose catch was while using a bowl gouge. I viewed the Stuart Batty videos sometime ago and really liked them. However I lost the link and could not find them. Thanks for the link. I’m going to do my home work before starting bowl turning again. The first bowl is certainly beyond hope – too many missing parts.

-- socrbent Ohio

View Nubsnstubs's profile

Nubsnstubs

826 posts in 1197 days


#5 posted 03-07-2015 04:06 PM

How thick is that bowl shown in 2 pieces? If it’s thick enough, you could glue it back together, and drill in some 1/8- 1/4” dowel holes, and insert them with glue. Then remount, and re-turn until you like the thickness. Go to youtube,, put in Chas Thornhill, and watch his video on the Elm Bowl. He salvaged a piece of wood that most would use for firewood. That method is the cleanest I’ve seen for recovering a bad or broken form.
Like Lee said, no dovetail, and index off the face of your jaws….... ................. Jerry (in Tucson)

-- Jerry (in Tucson)

View gwilki's profile

gwilki

121 posts in 941 days


#6 posted 03-07-2015 04:57 PM

If it were me, I would use them both as a lesson for the next time, and use them for firewood. You could glue a waste block on the second one and make a go of it, but it may well be a bigger pain than the final product is worth.

As to the jaws, I have what I believe to be the same jaws – at least from what I can tell by your pic. According to the nova site, they are dovetail jaws. LeeMills has said that they are not, so you had best check whatever manual came with them. Here is the link to the Nova site that shows the ones that I have.

http://www.novatoolsusa.com/NOVA-50mm-2-Jaw-Set-JS50N.htm

-- Grant Wilkinson, Ottawa ON

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socrbent

419 posts in 1737 days


#7 posted 03-07-2015 05:13 PM

Grant – unfortunately the first bowl also has some missing parts that IMHO make trying to repair it not worth the effort. Thanks for the link.

-- socrbent Ohio

View LeeMills's profile

LeeMills

273 posts in 768 days


#8 posted 03-08-2015 02:38 AM



As to the jaws, I have what I believe to be the same jaws – at least from what I can tell by your pic. According to the nova site, they are dovetail jaws. LeeMills has said that they are not, so you had best check whatever manual came with them. Here is the link to the Nova site that shows the ones that I have.
- gwilki

That site does have the jaws but go here to check for instructions. Scroll down to the Spigot Operation and then Forming the Spigot.
http://teknatool.com/products/Chucks/G3/Downloads/G3_Manual.pdf

By Nova, spigot mount refers to endgrain mounting such as vases, candle holders etc. Spigots may be straight (Pin, 25mm bowl, 35mm bowl), serrated (35 and 45mm spigot jaws and 100mm power grips, lips (50mm, 70mm bowl), dovetailed 100mm bowl and prowergrip, and 130mm bowl).
Almost every set has an exterior dovetail. The larger (100mm and 130mm) are the only ones I know of with a true interior dovetail.
Bowl mount on the other hand refers to mounting into a recess for expansion. Well except for the 100mm powergrips which have both an interior and exterior dovetail as well as serrations for spigot mount.
So look at your jaws to see what they have.

This is based upon the Nova chucks and jaws I have from mid 90’s to today.
With all the the 50mm jaws I have the attached shows how they are made. The lip is only about 4mm long (1/8”) and 1.5 mm wide so they will bite in easily.
The diagram shows what may happen if you cut a dovetail in a spigot for jaws only with a lip.

-- We cannot solve our problems with the same thinking we used when we created them. Albert Einstein

View gwilki's profile

gwilki

121 posts in 941 days


#9 posted 03-08-2015 11:34 PM

Socrbent: I was wrong in believing the jaws were made for dovetail tenons. Leemills is correct. I pulled out the instructions that came with my jaws. I’ve not used them in years, so I needed to refer to them again. They are made for dovetail spigots, but not tenons. I hope that you did not rely on my information to try another bowl.

-- Grant Wilkinson, Ottawa ON

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socrbent

419 posts in 1737 days


#10 posted 03-09-2015 01:37 AM

Grant – yes, I read the directions today. Part of my problem lies in not reading those directions and following what I saw in some online videos which were probably for different jaws.

-- socrbent Ohio

View LeeMills's profile

LeeMills

273 posts in 768 days


#11 posted 03-09-2015 03:47 AM


They are made for dovetail spigots, but not tenons.
- gwilki

I assume that was a typo (spigots). A spigot and tenon is the same thing, just different verbiage.
A recess, which is expanded into, is sometimes called a rebate or mortise by some folks.
Almost all Nova jaws have a dovetail for expanding into a recess; only a few (100mm and larger) have an additional internal dovetail for a contraction grip.

-- We cannot solve our problems with the same thinking we used when we created them. Albert Einstein

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