Another Power Drawbar Thread

kb58

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I have a PM-935 mill on the way and thought that a power downfeed would be a fun project – not necessarily a requirement, but sometime fun to build. Reading through various threads, there are concerns about not dinging up the spindle nut, in addition to ensuring proper engagement, as well as the problem of the tool either not releasing, or dropping onto the work. Some people say that they switched to an ER32/R8 collet holder as a solution, and on this I need clarification.

I believe that the ER32 holder is intended for CNC use, but some people use them on manual mills to avoid having to mess with the drawbar. I'm guessing that using a spanner wrench on the collar as opposed to reaching up to the spindle nut is the reason why. Since this is my first mill, I don't have any tooling yet, so it makes no difference whether I buy R8 or ER32 collets.

Keep in mind I know just enough to be really dangerous, so please correct any of my thinking.
 
I Googled "ER-32" and see that there are quiet a few ER-series holders. The ER-50 is supposed to grip down 2mm instead of 1mm (like the -32 does), but I suspect it probably costs a lot more.
 
If the spindle is R8, there is no disadvantage in doing ER40 instead of ER32.

If nose height is ever a problem then direct use of R8 collets is ideal.
Direct R8 collets have 1 less ways to create runout.
 
No downside to going with ER40 at all? If there is no downside, I'll certainly look into it, thanks.
 
The downside is that the adapter takes Z space and can introduce runout. I use the Shars ER40 adapter on my Bridgeport and the added runout is small, meeting the spec they give.

Get some good collets, I use Techniks, but there are a few known good brands.

I prefer working with the ER40 over the R8 with the drawbar and that ER40 are self extracting. I also use them on the lathe and already had them for that use. I also have a small selection of R8 if I need the space, but that hasn't been an issue for me.
 
Very well, sir, I will look into both. I assume that with this, the whole drawbar thing is avoided since the attachment method is in the adapter. Thanks!
 
A couple more questions. What do you do use to chuck drill bits, an ER40 collet, or a drill chuck? If a drill chuck, did you find one compatible with the ER40 adaptor, or do you remove the ER40 adaptor and install an R8 drill chuck only for drilling?
 
I may have answered my own questions; I'm not finding any drill chuck that fits an ER32 or 40.
 
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I may have answered my own questions; I'm not finding any drill chuck that fits an ER32 or 40.

You would just use a chuck with a straight shank and insert it into a collet.
 
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