I find that this cuts my 4 jaw chuck indicating time to less than half.
Thank you for your post.
Please forgive if I am missing something here? But this does appear to be a lot of work and trying to reinvent the wheel. I appreciate there is always more than one way to skin a cat.
There is no explanation in the video on how the stock was finally clamped concentric to the lathe centre line? Are you relying on the similar pressure being exerted on each jaw via the Chuck key, once the mandrel is removed?
The setting up of the four jaw Chuck can be easily achieved using just a 6” rule on the Chuck. The 4 jaws are set in position and a rule measurement taken from a known reference point on the Chuck. This reference point could be the outside of the Chuck itself or the rings in the face of the Chuck. Once roughly at the correct diameter/AF the distance between the opposite jaws can be measured again with the rule, the stock being machined can be slid into the jaws and lightly tightened. This will get you with in 0.010” / 0.25mm (even on a bad day.) Then you can use whatever method to trim the stock perfectly to the centre line of the lathe with a DTI.
I have added a link to show the process I use. Although the video shows rectangular stock being clocked it is exactly the same principle for clocking square bar.
I hope this is of interest and helps you in the future when clocking up stock in a 4 jaw. This will also help save you valuable time and materials, in making a mandrel for every size of stock you are likely to need in the setup of a 4 jaw Chuck.
Method for clocking rectangular or square in a four jaw to a known reference point
The Home Engineer.
https://littlemachineshop.com/images...4-jawchuck.pdf as the last few paragraphs of the pdf say, you can center a round bar, open two adjacent jaws a bit, and put a square (or octagon) bar of the same size in and tighten the two sides to be well aligned.
Thank you for the reply.
As WmRMyers has pointed out there are 4 jaw self-centring chucks.
A self centring 4 jaw is only as accurate as the stock being held. I often have to use shim to get all four jaws to contact a stock piece of square material. So my first choice for accuracy would be the 4 jaw independent chuck.
Where I find the 4 jaw self centring chuck really useful, is when several components need a shaft turned on a piece of square stock and the square is then required to to be machined in a second operating concentric to the shaft. This can save material and time rather than machining all from round stock. Or where the concentric accuracy is not critical ie: tee-bolts etc.
Therefore the 4 jaw self centring chuck is not often mounting on the lathe.
Another method is a lot more expensive but I find even holding square stock this is very accurate. Commercially made square collets like the 5C system or the Crawford multi-bore collets which I find to be very accurate. This accuracy is probably due the the amount of collect contact area with the stock. But again very expensive due to the amount of collets needed to cover stock sizes. Let alone purchasing the chuck body.
many thanks again but unfortunately the cheapest way to get square stock to run true is to setup in the 4 jaw independent chuck.
We all have to find away that suits are personal budgets and there is always more than one way to get the same result in Engineer.
The Home Engineer
Centering work in the 4jaw can be made much less tedious with a few homemade tools and a straightforward procedure. You may want to read my procedure here...
Centering work in the four jaw chuck
With this procedure, another dead simple addition can make centering polygonal stock much easier...
Centering aid for polygonal stock
Home Shop Freeware
mr_modify1 (Dec 31, 2021)
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