[Windscreen]

Hello all:

I'm considering the purchase of a bed mill that currently has an ISO 40 spindle. It is currently a manual mill that I plan to build a CNC system for. As best I can tell, ISO 40 in this case means DIN 2080, which seems to be the metric equivalent of a NMTB 40.

Seeing as how ISO 40 tooling is not very common in the USA, I would like to convert it to something more readily available. My first thought was NMTB 40, but based on the specs I found here, I'm not sure that is possible with a simple draw bar change. The OD of the cylindrical chunk on the back of the taper is about 4 mm larger on NMTB. I'm assuming the spindle has a fairly close ID pilot in the spindle and thus the NMTB 40 wouldn't fit all the way in. Anyone know if that is true, or likely true?

So, I think my next option would be to go to CAT 40 tool holders, since they don't have the extra "tail" on the back of the taper. I'm going to need to make a custom draw bar anyway, so there's no reason I can't make it longer to get decent thread engagement on a CAT 40 tool holder. Is there any reason this won't work? I've seen comments that the shorter thread engagement on a CAT tool holder isn't intended for a thread in draw bar, and the threads won't last. Is that just popular myth, or do folks really have experience pulling the threads out of a CAT holder when using a thread in draw bar repeatedly?

Thanks!
-Steve

[mactec54]

Windscreen

It would be a myth as both have the same type of heat treating, & are made from the same material

If the Cat40 all fit in ok, which it should, you would have the same amount of thread engagement as what you had with the other NMTB40, you just need a longer draw bar

The only problem you might have is the thread size, Cat40 have 5/8-11 inch thread the BT40 have 16-2 metric thread, the draw bar diameter might be a problem at 5/8 diameter, you can still get the NMTB 40 tooling New & used, Ebay is good some times, MariTool MSC ENCO & others all sell new tool NMTB 40 tool holders

[Windscreen]

Thanks much for the reply, mactec!

The difference in major diameter of the two threads is only 0.125 mm. Are drawbars normally guided that closely to the spindle ID? That was something I didn't expect. I guess the back-up plan will be to go with BT40 tooling and a longer M16 drawbar.

-Steve

[DareBee]

I have used all 4 in various machine over the years without issues. Different drawbars or pullstuds is all.
Doesnt mean I am right just that I had no issues