Quote Originally Posted by handlewanker View Post
Hi, I quite agree with your choice...….. if it works out OK it'll be quite neat.

The long job part is one thing you would gain advantage from a 4th and servo drive with a through hole.

I see you are opting for 5C collets...…..one problem with 5C is that it needs to have exact size collets for the material holding and a draw tube too tightened from the end which makes the 4th spindle diam and bearings a bit on the large size.

I think I would go the ER40 collet option....25mm diam material size is handy..... as it has a squeeze down factor of a mm and so can cater for raw material diams a few thou undersize.....I've never found any bar stock in cold rolled to be an exact size.

My personal preference for the 4th I'm building is an 80mm diam 3 jaw chuck with an option for a 125mm 4 jaw chuck too......the main reason is the large through diam.

One problem with those chucks is they are rated at max 4,000 rpm but as I won't be doing any turning for me it won't be a problem.
Ian.
5c has its ups and downs for sure. Like you mentioned, it needs exact collet sizes, although it seems to have enough give to handle standard stock sizes. They are supposed to handle +/-5 thou. One advantage of 5c over er is that they can grip onto short parts right at the nose. Er collets collapse at both the front and rear so if you try to grip something right in the nose, it will collapse at the back and not grip correctly. 5c is also nice because it's extremely versatile. Any attachment you can think of with 5c on the back of it. Expanding mandrels, large step chucks, 3,4,6 jaw chucks, flat fixture plates, emergency collets, list goes on, including a 5c-er40 attachment which i will most definately have for gripping any size I want. Bit more run out in the 5c-er40 attachment vs just an er40 chuck, but not much. The draw tube is also something that adds pretty huge capability once investing in a pneumatic closer. A bar puller attachment is simple to add, then you can crank out continuous parts unattended, as many that will fit in the bar stock.