Bridgeport/Clone NT30 Spindle Questions...

K

klandrith

Registered
Registered
Joined
Jan 5, 2021
Messages
6
Hello,

I have a Kent KTM-3S Bridgeport Clone that I purchased used that I am going to be cleaning up and repairing minor things on soon. I plan to swap out the R8 spindle for an NT30 spindle. Kent has these in stock with bearings already pressed on and ready to go (with ABEC 7 bearings). I may get my own spindle from Taiwan without bearings, if I can hunt down some ABEC 9 bearings that aren't a gazillion dollars and have the spacers ground to match. Not sure on that part. Advice is welcome.

I would like to utilize BT30 tooling as it (apparently) is cheaper to get a hold of. Now I know that the only difference between the two is the thread in the top of the holder, and I can simply use a metric threaded drawbar. However, I was wondering if it is possible to use a pedal type claw gripper instead with some belleville on top of a custom made drawbar and then utilize an ATC type air cylinder power drawbar setup. I'm not sure on the dimensions inside of these spindles and what the wall thickness is in various spots.
 
I'm at a loss why you would prefer the BT30 over R8??? Are you a hobbyist or do you own a machine shop doing production work? R8 is by far the most popular on Bridgeports and clones as most users are very happy with it.

Just curious...
Ted
 
Good question. I am just a hobbyist. I am going to be doing a CNC mill in the future (not the knee mill), and would like tool compatibility between the two machines as that one will have a BT30 spindle. Just trying to plan ahead to reduce redundant tooling. Its going to be awhile before the CNC project, so again, none of this all is set in stone or anything. I just thought it would be nice to have tool compatibility between the two machines further down the road when switching between projects and such.
 
Your mileage may vary, but I use R8 collets for 95% of my work. I have drill chucks and end mill holders that are R8, but very, very seldom use them. I do have a small carbide insert face mill I use occasionally, but that's really about it. My main usage drill chucks are mounted on straight shanks and I hold them in collets. Well, really thinking about it, maybe 98% of my work is done with collets! :)

A new spindle with bearings (or even without) is not a cheap way to go vs buying a R8 collet set. I would also think that having R8 would maintain a higher resale value. I personally would not want a Bridgeport with anything but a R8 taper.

YMMV,
Ted
 
Thanks for the input! Maybe I will just stick with R8, but hunt down some better bearings and replace the ones on the spindle if I can find some. I hadn't given a thought to resale value at all. You never know what happens down the road, I had to sell all my tools off during my divorce, including my last knee mill...The bearings in the mill aren't loud, but it is the high speed 6000rpm step head version and I would prefer good fresh bearings for aluminum work, and I might as well replace them while I am going through the head doing maintenance and checking everything. You make good points, I could just stick with all straight shank tooling where I can, and that would be able to transition over to the CNC mill with BT30 later on. The mill isn't very old at all and was from a junior college machine shop, so the ways have virtually no wear at all along with the table, but I don't know how prudent they were about filling the head up with oil so I definitely want to inspect it. The only real wear on the machine is cosmetic. I plan to have the machine for quite a while and want it in good condition starting out. Thanks again for your advice.
 
For me, I go by the old saying... "If it ain't broke, don't fix it!". I would suggest running it as is and see if the bearings really need replacing. Replacing spindle bearings is not a trivial project. Improper installation can cause a lot of problems.

Run it. Check the spindle taper (rotating it by hand) with a tenth's dial test indicator and check run out. If it's within a tenth or two and runs quiet without excessive vibration I would run it the way it is. Also, remember noise in the head more likely can be caused by any of the other bearings involved in drive system, especially if it's a variable speed head.

Just my two cents,
Ted
 
Technical Ted said:
For me, I go by the old saying... "If it ain't broke, don't fix it!". I would suggest running it as is and see if the bearings really need replacing. Replacing spindle bearings is not a trivial project. Improper installation can cause a lot of problems.

Run it. Check the spindle taper (rotating it by hand) with a tenth's dial test indicator and check run out. If it's within a tenth or two and runs quiet without excessive vibration I would run it the way it is. Also, remember noise in the head more likely can be caused by any of the other bearings involved in drive system, especially if it's a variable speed head.

Just my two cents,
Ted
Click to expand...
Good advice. I wanted to check spindle run out when I bought it, but I didn't have a good dial indicator to take with me, so I just listened to it run. It was only a little noisy at the 5440rpm. And yes, you are correct about head noise from other bits. Its a step pulley head. My plan isn't to go through it and replace everything, simply to make sure everything is clean and lubricated properly more or less, and repaint it along with adding a few accessories here and there. I'm definitely not pulling the lower head assembly apart at all, only the top half, as I will have to anyway when I repaint everything. I've been watching the H&W Machine Repair videos on YouTube, and I'm not about to mess with all the bits in the lower part of the head assembly without good reason. The power downfeed, kickout, etc work perfectly as is. The original idea was the convert it to CNC, but after running up the costs, and considering the limitations of a CNC knee mill, going with another platform for a CNC mill was more cost effective and made more sense for the future. That was where the original idea for the 30 taper tooling came in to maintain accurate tool heights.

I do have another question though that maybe you can help me with. The original Bridgeport J heads have grease ports for lubricating various parts, however the Import heads like I have only have two oil ports, my old Acra mill was the same with the same style high speed 2 speed motor head. Unless of course I'm blind - I can't really give it a good look now because I coated the mill with spray cosmoline and wrapped it in celophane to protect it until I tear into it - even though it is sitting inside, it's in an unheated shop. Is this an issue of the import heads are greased at the factory, without provision for periodic regreasing, or is the lubrication system for the various gears and sliding portions simply different? I read through the Kent manual online for the machine and there was no mention of greasing in it at all. I wasn't even aware of this difference until I caught a YouTube video detailing Bridgeport J head greasing. When I took machine shop in college years ago, the only vertical mills we had were Bridgeport J and 2Js, and some monster Cincinnatis, but I never paid attention to greasing the head as our teacher never mentioned it, we simply did the one shot luber everyday before use. Thanks again for the advice.
 
If it only has oil cups/ports then it's most likely to assume that it only takes oil. I have an Induma step pulley Bridgeport quasi clone that only takes oil. My Bridgeport variable speed mill takes oil for the spindle and has a small grease port for the hi/low shifting but no zerts. And it sounds like the manual doesn't state grease so probably just oil. You'll be able to tell once you open it up and do your cleaning, which is a good idea.

The Bridgeports I ran at work years ago didn't need greasing either. But, there are different vintages and minor differences over the years.

Maybe post a new post asking other Kent mill owners about their maintenance. Not sure if there is a better sub form to put your post in or not; you might want to look. But, include Kent mill in your post question and you'll probably get some good feedback.

Ted
 
I vote for 30 taper, much easier to change tools due to a much shorter shank and the steep taper, I have two mills that use 30 taper and vastly prefer it over R8.
 
You must log in or register to reply here.
Back
Top