Modify 35mm Nova Bowl Jaws

[Oldgreybeard]

330228I am considering buying a set of 35mm Bowl jaws for my Supernova 2 chuck. My problem is that the jaws have an external dovetail but no internal dovetail for holding a small spigot in contraction mode. This is illustrated in the image of my 25mm jaws wich are essentially the same profile.

There is a 35mm Spigot jaw set, but this only has a serated internal profile and is not suitable for holding a 3 -4 mm deep spigot on the bottom of small boxes. Since the proposed box diameters are approximately 40 - 45mm, IMO the external dovetails are too large to use in expansion mode without wasting valuable wood. My problem with the smooth parallel internal profile on these jaws is the lack of clamping force on the small spigot: 1 twitch and I have an instant UFO.

I am proposing to have the internal profile of the new jaws modified to provide an internal dovetail as indicated in the above image. This raises 2 questions (at least) -

1. Is my technique wrong and I don't need to modify the jaws? I am ready to be educated if this is the case.

2. The existing jaws have a 15mm thick "leg". Can I safely reduce this to 10mm?

Theory suggests that the proposed modification is practical - the remaining thickness of the leg at its thinnest point will still be almost double the thickness of the 25mm jaws and also of the 50mm jaws. I want to increase the minimum capacity in contraction mode from 9mm to about 20mm as this will increase the area of the jaws which are in contact with the 30 mm spigot.

I spent about an hour at Carba-Tec yesterday and we checked every version of the Nova range and found nothing which matched the design I was looking for - which suggests my technique might be the problem.

I would appreciate any advice. I don't want to spend money needlessly on new jaws and machining if there is a better solution.

Bob

PS. Many thanks to for his videos on chuck maintenance. The Bonhan chuck now looks presentable:2tsup::2tsup:

[Paul39]

Bob,

Here is some discussion about serrated and smooth jaws:

http://oneway.ca/chucks/accessories/no2_jaws.htm

Their tower jaws are smooth on the front edge with serrations further in:

http://oneway.ca/chucks/accessories/tower_jaws.htm

You might consider making a longer spigot to grab with the serrated jaws and then part the box off the spigot when you are finished.

I do bowls, some out of balance, roots and stumps, and like to have a firm grip on the blank. I then turn off the spigot and sand.

I have had enough incidents with expanding in a recess that I now only make a nice big spigot and grab it with a serrated jaw.

You could modify the jaws yourself using a high speed steel scraper on the tightly closed jaws. Go in slowly and resharpen when the cutting slows down. Get the tool rest 3 - 5 mm from the jaws. Around 800 RPM for cutting speed.

Doing it yourself, you can do a minimum cut and see how well it holds a blank, repeat to your satisfaction.

I modified a grade eight 33 X 3.5 mm nut to go on my Hegner spindle. I was quite surprised to see how well a HSS scraper removed steel.

[Oldgreybeard]

Bob,



You could modify the jaws yourself using a high speed steel scraper on the tightly closed jaws. Go in slowly and resharpen when the cutting slows down. Get the tool rest 3 - 5 mm from the jaws. Around 800 RPM for cutting speed.

Doing it yourself, you can do a minimum cut and see how well it holds a blank, repeat to your satisfaction.


Thanks Paul. I have used a HSS scraper to true up the face of the jaws on my old chuck - didn't think of doing this. Would it be possible to use a HSS drill to drill the centre to 20mm and then scrape the internal face to form the dovetail?

I agree with the better holding strenght of the serrated jaws, but blanks are cut to size ( more correctly offcuts) and only provide a maximum of 5 mm top & bottom for spigots. Guess I could decline the offer of the offcuts and buy new stock :no::no:

Bob

[turnerted]

Why don't you just hotmelt glue your blanks to a bit of scrap wood then you can cut a tennon on it to suit your existing jaws?
I nearly always do this when making boxes to save on wood.
Ted

[Oldgreybeard]

Thanks Ted. I do have a hot melt glue gun, but have not been confident that it would have sufficient strenght. I will give it a go.

Bob

[turnerted]

Bob
Zap your scrap tennon block in the microwave for 30 seconds before putting a glob of glue on it. It should be almost too hot to pick up and the glue should bubble when you put it on . Hold your blank in your chuck and use your live centre to line up the scrap tennon . Work quickly.If you are impatient like me,as soon as the oozed out glue has set, carefully remove from the lathe and stick the whole assembly in the freezer for 10 minutes . True up the dovetail if necessary.
Ted

[Mobyturns]

I am proposing to have the internal profile of the new jaws modified to provide an internal dovetail as indicated in the above image. This raises 2 questions (at least) -

.....
I would appreciate any advice. I don't want to spend money needlessly on new jaws and machining if there is a better solution.

Bob

PS. Many thanks to for his videos on chuck maintenance. The Bonhan chuck now looks presentable:2tsup::2tsup:

I would not modify this jaw set as it is not designed for use in contraction mode. NOTE that the jaws only have one set of cap screws on the outside so when a small object is held in contraction mode the leverage against the cap screw will eventually cause problems by bending the jaw outwards and stressing the cap screw. Recently there was post about a jaw flying from the chuck when used as you propose to.

Look at Vermec's ER25 & 32 collet chucks - far safer way to hold small spigots for spindle work and a very accurate method.

For the small boxes you wish to turn - why not make a jamb chuck? OR you could make some jaws from the NOVA soft jaws OR a set of ancillary wooden soft jaws but make sure you use good sound timber, align the grain for max strength and use two cap screws.

[Oldgreybeard]

I would not modify this jaw set as it is not designed for use in contraction mode. NOTE that the jaws only have one set of cap screws on the outside so when a small object is held in contraction mode the leverage against the cap screw will eventually cause problems by bending the jaw outwards and stressing the cap screw. Recently there was post about a jaw flying from the chuck when used as you propose to.

Look at Vermec's ER25 & 32 collet chucks - far safer way to hold small spigots for spindle work and a very accurate method.

For the small boxes you wish to turn - why not make a jamb chuck? OR you could make some jaws from the NOVA soft jaws OR a set of ancillary wooden soft jaws but make sure you use good sound timber, align the grain for max strength and use two cap screws.

Thanks Mobyturns, I had over looked the stresses on the screws. You are absolutely correct.!!

Time for a rethink along the lines you and TurnerTed have suggested.

Bob

[QuarkVI]

The Nova mini spigot jaws get around the having only one screw problem but don't seem to have the internal dovetail you were after.
I was eyeing a set of them to use for smaller pieces like finials etc.

I have been using the hot melt glue method for making smaller boxes - haven't tried putting the sacrificial tenon in the microwave though.

[chuck1]

Most lidded boxes I turn I friction chuck. So I keeps lots of scrap timber/craftwood for chucking! But you have to accurate with your turning.

[hughie]

I have modified some of my jaws in the past to suit my individual purposes. However Mobyturns makes a good point, the jaws are not heavy duty. They are probably good for pens and the like. So what you hold with them, be mindful that they wont hold big blanks. If you choose to do the mod I would be looking at the smallest amount of dovetail I could get away with.

One the major problems to doing this sort of change is they have one screw to hold the jaws. Which is fine on expansion, but put the stress in a different place on contraction.You will relying on the keying to the underside of the jaw to prevent twisting. But will have increased the leverage to the screws due to their position at the rear of the jaw. This increase will be sizable due to the torque you can exert with tightening.

[Paul39]

I agree with Hughie's post # 11 above.

[NCPaladin]

I have thought of doing the same thing myself as the 35mm bowl, 25mm, and pin jaws have identical spigot sizes. I am going to go about like you stated or about 7/8, which would give me 7/8 to 1-1/2. As long a the items is small I do not think there will be too much stress. I plan on using a carbide cutter for steel (machine shop type) - about $3-4 on a 1/2 X 4" shaft. No Nova jaws have a dovetail on the interior until you get up to the 100mm. The 35mm spigots may be the ticket. I already have 1.5" delrin rod. I plan on drilling it out in 1", 1-1/8, 1-1/4, 1-3/8 then making a jig to cut a kerf on the table saw. Each "collet" will be as long as the jaws are tall (abt. 1-3/8). Probably need to rough up the collet in and out to give more bite. You can make the collets from a good wood and get many use.
To me the best for your needs may be the soft jaw.