Three jaw scroll chuck jaws

[old martParticipant @oldmart]

Roger showed me a little Proxon chuck that he had bought for a wood lathe. The type that used tommy bars rather than a key. I noticed straight away that the jaws were the reversable type so only one set is required. The jawteeth are bi-convex rather than convex-concave. I had heard of the type, but never seen one before, and it has just occurred to me that the jaw numbering might be different depending which way round they were fitted. Do they have two numbers on each jaw?

[Peter Cook 6Participant @petercook6]

Not sure if they have two numbers on the Jaws, but they are inserted in different order. Sherline have a Good description at https://sherline.com/wp-content/uploads/2015/01/1040inst.pdf

[JasonBModerator @jasonb]

No1 stays the same 2 & 3 swap if I remember right from my Unimat, will check later.

[JasonB]

On JasonB Said:

No 1 stays the same 2 & 3 swap

That is perhaps missing the wood for the trees.

You could quite equally say No. 2 stays the same and 1 & 3 swap or No. 3 stays the same and 1 & 2 swap.

The logic would be like reversing a three phase motor. Swap any two of the three.

—

Now, what if you had a self-centring four or six jaw chuck with the same jaw septup?

[old martParticipant @oldmart]

Thanks, next time I see Roger, if he hasn’t worked it out for himself, I will be able to tell him 1-2-3 normal and 3-2-1 when reversed according to Peter’s link. It must be tricky for the makers to grind the jaws so that both inner and outer surfaces are true to the axis whichever way round they are fitted.

[JasonBModerator @jasonb]

Just checked and it was not as I thought. It is jaw 2 that stays the same. but I don’t use that chuck much now.

In practice I don’t look at the numbers on any of my chuck jaws. I just look at the position of the “teeth” on the back and put the one with them nearest the end in slot 1 and work my way round.

[old martParticipant @oldmart]

I have just noticed while scanning ebay that four jaw scroll ckucks of 50mm diameter can also be obtained with reversable jaws.

[Author]

Posts