Jet BDB-1340 Lathe - 1,240 RPM Top Speed, Pulley Replacement, Motor Cooling Questions

Top spindle speed for this model is 1,240 RPM. That sure seems slow. Is it?

I'm replacing the stock motor with a 2HP 3 phase 4 pole motor and adding a VFD. It's a new motor with a Streans brake that I guess is old stock because it has class B wiring. Can I overclock it to say 90 Hz to get the top spindle speed to 1,860 RPM?

Also I just noticed the new motor has no fan because of the brake. It's sealed with no cooling fins. That doesn't seem good in any circumstance.

Lastly the original motor has a 2.25"-3.88" 2 step pulley with a 3/4" bore. The new motor has a 7/8" shaft. Unbeknownst to me 2 step pulleys are not common and I can't find one close to what I need. I never suspected that the pulley was going to be a problem. Boring the existing pulley out would leave the bottom of the 2" pulley 1/8" thick. That seems to be pushing it. Any suggestions?

If that lathe has tapered roller spindle bearings like the one I had years ago, it will not like spinning at higher than standard speed for very long at all. Mine got uncomfortably hot even at 1,200 RPM. Perhaps if you played with the preload and oil viscosity, you could pull it off.

1/8” wall at the bottom of the V pulley seems ok unless there is a key way. Draw it up. It still might be ok. It’s not a high-stress situation. Besides, you’ll have a lathe and can turn up a bigger pulley and change the belt to accommodate.


Sent from my iPhone using Tapatalk

I doubt there will be any turning application you will come against, using that machine, that will even suggest higher turning speeds. Even collet work will have the machine shaking around and howling.

1200 rpms will be fine!

Unlikely to need to go to 1800 RPM, I have only used the higher speeds for polishing. typically turn at speeds under 1400 RPM. Also depends on what cutting tools you are using, carbide inserts require higher speeds. A lot of gunsmith use this particular belt drive Jet, felt to be more optimal due to the belt drive in the head dampening motor vibrations. Never hear of anybody wanting it to go faster, I have built a few VFD systems for individuals with the smaller jet 1024 lathes.

You are most likely limited by the bearings as to the the top speed, probably something like 1600 RPM for short periods might be acceptable. But if the bearings heat up and the tolerances change you could seize the bearings.

As far as the brake motor, should be ok to go to 90 Hz, I would remove the mechanical brake assembly. Cooling is not typically a problem at 90 Hz, but it depends on the motor and the duty cycle. You would have been probably been better off with a conventional TEFC or TENV motor which can be picked up at very reasonable costs. I would use a single belt motor pulley, something like a 3" and let the VFD give you the low/high speed range. Using 30-90 Hz, you will top out at around 1500 RPM should you need it. I do this all the time with similar lathes that have two motor belt ratios, never have had a power issue.

Do not buy a cheap VFD, these are often lacking the ability to add an external braking resistor that should be used with lathes if you use electric braking. They often are also lacking programming parameters and motor tuning parameters.

I have basically the same lathe and have done just what you are proposing and can attest to the fact that the bearings do not really like spinning much faster than stock. With enough preload to avoid chatter they heat up quickly at those speeds. I currently have my VFD and belts setup to limit to 1600 rpm for doing small work but I pay attention to the bearing temps and don't run it for long periods at those speeds.

I found the same issue on my pulley so I went with a 3.15" OD single pulley for the motor. With the VFD I wanted to eliminate the motor belt change anyway. I originally ran it in the faster setting to get around 1800rpm but given the issues discussed above I moved it to the slower setting. I still get 1600rpm at 90 or 100 Hz.

I'm happy with my Lapond VFD from Amazon. Their "improved" version is sensorless vector and braking resistor compatible and is under $180.

Thanks for the responses. I have many questions.

Let's start with the spindle bearings. I had no idea they had such RPM limitations. I thought the feed/threading drive train would be where the problems might arise. Is it because the bearings are cheap? The amount of pre-load required? Or both? I was looking at the specs of some Timkin equivalent bearings that I don't think were all that expensive, and they were rated up to 5-6K RPM.

The limitation is not necessarily the bearing itself, but the lubrication, loading and dissipation of heat. Typical splash lubrication lathes max out at around 2500 RPM, but heat buildup and getting lubrication to the bearing w/o a pressurized system can lead to bearing failure. You also have higher lateral loading, thermal expansion, and probably a host of other factors. I run into this constantly with people installing VFDs and wanting to run their mill/lathe at 1.5-2X it rated speed, speaking to the manufacturer they usually say 20-25% max, there are many factors. There are also other components in the drive system that may not be rated for the elevated speed. You are also limited by chuck speed rating, semi-steel 8" chucks often have a maximum speed rating of 2000-2500 RPM. Poorly balanced ones are much lower.

JCByrd24 gave his experience/recommendation with essentially the same lathe. Of course you can do whatever you want, but I can't see the need to turn above 1600 RPM on a manual lathe of this size. Do you have a particular circumstance for the need of a higher speed?

My no-name 13 X 40 lathe has 8 speeds and the highest is 2,000 rpm. I have yet to use it on a job. I tried it once and it scared the heck out of me.

Above posters are right about overhearing the spindle bearings. It's a real consideration.

mksj said:

Do you have a particular circumstance for the need of a higher speed?

Click to expand...

No, I was just surprised by the max RPM. As long as I was adding a VFD and changing pulleys, I thought I'd ask here if it was feasible to increase the max. Always better to have more than you need than not enough.

The general consensus is don't go above 1,400-1,600 so I won't. Thanks!

rklopp said:

1/8” wall at the bottom of the V pulley seems ok unless there is a key way.

Click to expand...

The keyway would have be re-cut. That might a bit much for my skill level. I might give it a try anyway just have a project.