Ok, so I know that if you need real accurate machining, then a collet chuck is the way to go.
A self centering scroll chuck is a fantastic tool but has bad reputation ( unfairly IMHO) for not being accurate enough for precision work.
I recently needed to use my previously unused 4 jaw SC chuck and once I machined the faceplate and got it mounted, I measured the accuracy.
(The accuracy of a scroll chuck has a gazzillion variables...the wear on the scroll and jaw teeth, the cleanliness of its parts and the diameter of the work to name a few. )
I started off with a clean and de-greased chuck. I knew that I wasn't going to get it perfect over the entire jaw opening range, so I only measured the error between 6mm and 14mm diameter workpieces.
My error was varying between 0.08mm and 0.15mm. Not a massive amount but certainly not great and not a good as I need.
First I set the jaws so that they were just 'inside' the bore of the chuck body. Then I marked the faces of the jaws with marker pen. Then set the machine to Warp Factor 5. ( Full Speed :wink: ) Centrifugal force to keep the jaws tight on the scroll.
Using a Dremel type handpiece in the toolpost, I took minute passes over the spinning jaws. It took around ten back and forth passes with out changing the grind cut depth until there was no more tiny sparks.
I continued this till all the marker pen was removed from all the jaws.
Result? With a dial indicator I get an error of 0.01 to 0.02mm with test bars of 10mm and 20mm diameter respectively.:biggrin:
I then removed the chuck, thoroughly cleaned and lubed it and stuck it back on. Almost identical results!!! Neddless to say, I'm very happy!!:biggrin:
I read this method of truing a SCSC on the web a few years ago, but I didn't fully understand how it worked till now. I wish I had thought about it years ago, cos it's actually a LOT simpler than it might seem.
If you'd like to have a go, but can't figure out something, then please ask and I'll try and explain it better.
A self centering scroll chuck is a fantastic tool but has bad reputation ( unfairly IMHO) for not being accurate enough for precision work.
I recently needed to use my previously unused 4 jaw SC chuck and once I machined the faceplate and got it mounted, I measured the accuracy.
(The accuracy of a scroll chuck has a gazzillion variables...the wear on the scroll and jaw teeth, the cleanliness of its parts and the diameter of the work to name a few. )
I started off with a clean and de-greased chuck. I knew that I wasn't going to get it perfect over the entire jaw opening range, so I only measured the error between 6mm and 14mm diameter workpieces.
My error was varying between 0.08mm and 0.15mm. Not a massive amount but certainly not great and not a good as I need.
First I set the jaws so that they were just 'inside' the bore of the chuck body. Then I marked the faces of the jaws with marker pen. Then set the machine to Warp Factor 5. ( Full Speed :wink: ) Centrifugal force to keep the jaws tight on the scroll.
Using a Dremel type handpiece in the toolpost, I took minute passes over the spinning jaws. It took around ten back and forth passes with out changing the grind cut depth until there was no more tiny sparks.
I continued this till all the marker pen was removed from all the jaws.
Result? With a dial indicator I get an error of 0.01 to 0.02mm with test bars of 10mm and 20mm diameter respectively.:biggrin:
I then removed the chuck, thoroughly cleaned and lubed it and stuck it back on. Almost identical results!!! Neddless to say, I'm very happy!!:biggrin:
I read this method of truing a SCSC on the web a few years ago, but I didn't fully understand how it worked till now. I wish I had thought about it years ago, cos it's actually a LOT simpler than it might seem.
If you'd like to have a go, but can't figure out something, then please ask and I'll try and explain it better.
