Converting R8 spindle to CAT40

mm58 · Sep 29, 2009

Hello,

I have an Induma knee mill (bridgeport style) that has an R8 spindle. Has anyone made a conversion - or even know if it's possible - to get a spindle that will accept the CAT40 toolholders. The reason I'm interested, is that I just came into a bunch of CAT40 holders and ER40 collets and I'd like to be able to use them.

Any input appreciated...

MIke

Doozer · Sep 29, 2009

I think Forrest Addy was contemplating this. At least that is what I think I remember reading. He is in General New or at HSM.

--Doozer

HsvToolFool · Sep 29, 2009

Please excuse this naive question...

I was recently looking at a used mill with an NMTB40 spindle. However, I then discovered that CAT40 and BT40 holders were much more plentiful on EBay.

I understand these systems all use the same taper. But I assume a NMTB spindle won't grip CAT and BT. Am I correct that they are not interchangable?

mm58 · Sep 29, 2009

Well... as happens so many times, right after I posted, I found and ordered an ER40 holder with R8 shank. So my need (or interest) in changing over to a complete CAT40 spindle is no longer necessary. I'll keep the CAT40 holders on the back burner in case I ever get a machine that takes them. Thanks for the replys.

Mike

Joe DAmico · Sep 30, 2009

HsvToolFool said:
Please excuse this naive question...

I was recently looking at a used mill with an NMTB40 spindle. However, I then discovered that CAT40 and BT40 holders were much more plentiful on EBay.

I understand these systems all use the same taper. But I assume a NMTB spindle won't grip CAT and BT. Am I correct that they are not interchangable?

the taper on the nmtb, cat 40 and bt 40 are the same. The nmtb uses a draw bar and will not run a machine that uses a tool changer. the cat and bt 40 could run in a nmtb 40 splinde but you may need to chage the lenght of your draw bar. I'm not sure why you would want to. The cat and bt tooling is worth twice as much as the nmtb tooling. I sell alll 3 stlyes and get twice as much for the cat and bt than the nmtb. This goes for both the 40 and 50 taper tool holders.

Thank you
Joe

PixMan · Sep 30, 2009

Why 40 taper? Seems to me a 30 taper would be so much better-matched to the size and HP of a Bridgeport. I don't think a 40 taper would even fit a Bridgeport without a lot of extension and losing Z travel.

HsvToolFool · Sep 30, 2009

Joe DAmico said:
the cat and bt 40 could run in a nmtb 40 splinde but you may need to change the length of your draw bar.

Good to know it's feasible (if not trivial). Thanks!

Joe DAmico said:
I'm not sure why you would want to. The cat and bt tooling is worth twice as much as the nmtb tooling.

CAT40 seems common to smaller CNC machines, so it often appears in auctions and on the used marketplace. From that angle, prices are much lower than relatively scarce NMTB40 (especially when new). Of course, this is just my impression from recent window shopping.

I also suspect that compatibility with small VMCs would be a worthwhile convenience in a small shop. Who knows? Maybe someday I'll have one.

PixMan said:
Why 40 taper? Seems to me a 30 taper would be so much better-matched to the size and HP of a Bridgeport. I don't think a 40 taper would even fit a Bridgeport without a lot of extension and losing Z travel.

My desire to avoid R8 is for quick-change capability and Z-axis repeatability. I agree that accuracy or chatter-free hogging are not relevent. NMTB30 is adequate for manual knee mills.

Series II Bridgeports and Laguns offer 3HP motors and weigh around 3,000 lbs. Laguns offer NMTB30 and 40 taper spindles as factory options. The mill I found has a NMTB40 spindle, so my thoughts turned to CAT40 once I discovered that it's more common on the used market.

It's nice to know that it's feasible that I can run CAT40 in a NMTB40 spindle. How challenging such an adaptation would be remains to be seen.

Joe DAmico · Sep 30, 2009

If you are running a NMTB 40 tool in your machine know the only thing yoou will need to do is lenghten the draw bar. If you look at a NMTB tool holder it has a shouder on the draw bar end. If you look at a cat 40 it does not have the shoulder, this is where you would install the pull stud. You draw bar will end up short because it is looking for the shoulder. I do have number of the NMTB holder in both 40 and 50 taper. I sell them both for 20.00
Hope this helps you
Thank you
Joe

gbent · Sep 30, 2009

Bridgeport offered a factory 30 taper spindle. It used the Erickson QC 30 tooling. The toolholder was retained by a cap on the tool end of the spindle, so no drawbar was needed. R8 and 30 taper both have a 1 1/4" gageline diameter. The 30 taper has the advantage of being shorter and having positive drive lugs rather than the tiny dog point of a set screw.

The 1 3/4" gage line of 40 taper tools would extend the tool quite a ways further from the spindle bearings. I think you would end up with a weaker system than you would have with the smaller 30 taper.

taiwanluthiers · Oct 30, 2021

mm58 said:
Hello,

I have an Induma knee mill (bridgeport style) that has an R8 spindle. Has anyone made a conversion - or even know if it's possible - to get a spindle that will accept the CAT40 toolholders. The reason I'm interested, is that I just came into a bunch of CAT40 holders and ER40 collets and I'd like to be able to use them.

Any input appreciated...

MIke

No.

NT40/CAT40/NMTB40 is much larger than the R8.

Here is a side by side of a R8 tool, NT30, and NT40 tool. As you can see NT40 tool is quite a bit larger than R8.

And a bridgeport head probably does not have enough room to accommodate a NT40 spindle as the spindle needs a minimum diameter (the quill part) of around 3.5 inch (my mill has a quill diameter of about 90mm, so around 3.5 inch or so) because you need room for the spindle, the quill, and the various bearings. R8 is simply too small. NT30/NMTB30 would be a possibility if you can find a spare spindle to use.

If you have a bridgeport series 2 mill, then NT40 spindle may be a possibility, as they have a larger head.

Also a NT40 spindle (if you have not already found out by now) is much heavier than a R8 spindle.

Edit: So they do make NT40 spindles for Bridgeports... Found this on ebay

Bridgeport Milling Machine Tools NT40 Shaft Spindle Vertical Mill Parts | eBay

You'll have to figure out how to change the spindle and use the right bearings... I don't know if its original bearings will work as this spindle looks a lot beefier compared to the R8... But NT30/40 is a great spindle because they have positive drive keys whereas R8 does not. Also they are interchangeable with every other milling machine as all the various -30 -40 taper is the same. Meaning if you have a CNC machine you can just cut the knob off the NT40 tool holder and stick a pull stud in it, and it will work in the CNC. R8 is manual mill only.

1Set Bridgeport Mill Part Milling Machine NT40 Spindle + Bearings Assembly | eBay

NT40 spindle with bearing. You are going to want this as the spindle is quite a bit larger than the R8 spindle... so your stock bearing will not work.

moonlight machine · Oct 30, 2021

taiwanluthiers said:
No.

NT40/CAT40/NMTB40 is much larger than the R8.

Here is a side by side of a R8 tool, NT30, and NT40 tool. As you can see NT40 tool is quite a bit larger than R8.
View attachment 333409

And a bridgeport head probably does not have enough room to accommodate a NT40 spindle as the spindle needs a minimum diameter (the quill part) of around 3.5 inch (my mill has a quill diameter of about 90mm, so around 3.5 inch or so) because you need room for the spindle, the quill, and the various bearings. R8 is simply too small. NT30/NMTB30 would be a possibility if you can find a spare spindle to use.

If you have a bridgeport series 2 mill, then NT40 spindle may be a possibility, as they have a larger head.

Also a NT40 spindle (if you have not already found out by now) is much heavier than a R8 spindle.

Edit: So they do make NT40 spindles for Bridgeports... Found this on ebay

Bridgeport Milling Machine Tools NT40 Shaft Spindle Vertical Mill Parts | eBay

You'll have to figure out how to change the spindle and use the right bearings... I don't know if its original bearings will work as this spindle looks a lot beefier compared to the R8... But NT30/40 is a great spindle because they have positive drive keys whereas R8 does not. Also they are interchangeable with every other milling machine as all the various -30 -40 taper is the same. Meaning if you have a CNC machine you can just cut the knob off the NT40 tool holder and stick a pull stud in it, and it will work in the CNC. R8 is manual mill only.

1Set Bridgeport Mill Part Milling Machine NT40 Spindle + Bearings Assembly | eBay

NT40 spindle with bearing. You are going to want this as the spindle is quite a bit larger than the R8 spindle... so your stock bearing will not work.

He prolly figured it out 12 years ago when he posted......

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