Stepped chuck jaws

[Democritus]

Hi Guys,
I’m looking to get stepped chuck jaws. All my chucks are Record Power SC4. Record don’t seem to do stepped jaws, so is it possible to use the Nova stepped jaws on the RP SC4?
D.

 

[Linus]

I use both Record SC4 and Nova chucks and the jaws are interchangeable.

 

[Democritus]

Thanks , Linus
D

 

[Democritus]

Hi guys,
I took Linus’s advice and have bought a set of Nova stepped jaws. As Linus said they fit my RP SC4 chuck ok, although the Nova jaw manual says that Nova jaws are designed to be used on Nova chucks only, and cannot be used with any other chuck because of the possibility of serious injury.
Besides that warning, the only query I have is that the Teknatool chuck accessory jaw manual suggests maximum rpm (expanding and contracting) for each of their jaws. The stepped jaws has 684rpm for both. Other jaws in the collection have varying rates, e.g.50mm jaws from 684rpm expanding, and 1020 rpm in contraction. The highest recommended speeds ( 684 - 1440) are for the 25mm jaw set, the pin jaw set, and the 35mm jaws.
Why is this?
I know that speed should be determined ( amongst other things) by the size of the blank, but I often turn at more than 1000 rpm with my RP 50mm jaws in expansion .
Is there something about the holding power of Nova chucks that means they can only be used at comparatively low rpm?
Advice please.
D

 

[Doug B]

All my jaws are nova jaws & are at least 17 years old, I don’t remember any information on speed limits on there use when I got them, I’ve definitely used them at higher speeds than you are suggesting with no problem, perhaps it’s just an ar5e covering exercise

 

[Democritus]

Here’s the speed page in the manual.

 

[Fergie 307]

Does seem odd, especially when they come up with such a precise figure as 684 rpm. Presumably if you are rash enough to run it at 685 you will invalidate the warranty

 

[Doug B]

That does seem odd, perhaps with deaths caused by wood leaving the lathe unexpectedly seemingly on the increase (I heard of another only last week) they are covering there backs

 

[sneggysteve]

Same as Doug B above - all mine are Nova and no problems. Only when using the Cole jaws do I slow down on for obvious reasons

That reminds me, I have too many jaw sets and should put them up for sale soon.

 

[Democritus]

Cheers, guys. It’s a mystery why they state these very precise maximum rpms for their jaws. An even bigger mystery is why they quote maximum rpm for FACEPLATES both in expansion and contraction. How does that work? .....
I think I might drop them a line..
D.

 

[Linus]

Cheers, guys. It’s a mystery why they state these very precise maximum rpms for their jaws. An even bigger mystery is why they quote maximum rpm for FACEPLATES both in expansion and contraction. How does that work? .....
I think I might drop them a line..
D.

I'm slightly baffled as well. I just bought some Nova 25mm bowl jaws and the accompanying paperwork is the same as yours.

One point to note, Record jaws have a parrot beak grip on the compression side whereas the Nova jaws I just purchased have a straight grip inside, not even a dovetail. This may be why they are cautious about the speed.

 

[ChaiLatte]

The relationship between chuck jaw gripping force and rpm has been well studied in the metalworking world.

When you spin up a workpiece, the centrifugal force reduces the gripping force when the jaws are outside the material and increases it when inside the material.

You can buy grip force meters for chucks. The wireless ones work better if you want to measure force when the chuck is rotating.

For faceplates, which are generally large diameter, overspeeding could lead to material failure at the perimeter, hence the max. rpm.

Having a safe rpm on a chuck is no different to having a safe rpm on an angle grinder disk or saw blade.

See graph on this page for an indication of the relationship between grip force loss and rpm:

https://www.kitagawa.global/en/products/power-chucks/open-centre-chucks/b-210
See also:

https://prod.kiw.co.jp/mtools/item/data/PDF/gripforceset_en.pdf
The take away from the pdf file above is that jaw geometry contributes to the grip force and grip force loss.

 

[Democritus]

Thanks for your input, ChaiLatte.
I have no knowledge of metal working lathes, but appreciate that metal turnings breaking up or coming off such a lathe could be absolutely catastrophic, easily causing death or serious injury. Blanks coming off wood turning lathes have also caused deaths and injury, but these are, thankfully, rare events, and, generally, the results of break ups/detachment are usually minimised by good quality PPE. I think that most deaths in Woodturning have been the result of facial impact in turners not wearing faceshields.
I note that the Kitagwa B-210 open centre power chuck has a maximum (safe?) speed of 4200rpm.This far exceeds the rpm’s on even the biggest Woodturning lathes. It is no wonder that the gripping power of the metal turning chucks has to be so carefully calculated. I have never seen such calculations applied to our lathe chucks, but other woodturners on this site might know better than me.
My point about the faceplate rpm’ s was that faceplates cannot expand or contract. They are the size they are, and that’s it. Pieces could come off a faceplate, but that is another story.
D.