Improving a lathe spindle head.

[tonyfoale]

Your removal of the back gears puzzles me. They lock the spindle when trying to change the chuck or faceplate on a threaded spindle. They may not be needed for machining because of the VFD, however certain operations such as tapping would have much more torque with the back gears engaged with a higher motor speed.

No need to be puzzled, as I mentioned I almost never needed to use the back gears. I never use them to lock the spindle, my brutality to lathes does not extend to that. I made a tool to hold the spindle for chuck removal.
I do not need more torque for tapping, that could lead to broken taps. For that reason you can buy torque limiting tap drivers.

[MeJasonT]

looks like an impressive mod.
left wondering why you didn't just attach the motor in such a way as to use the existing gear train.

The degree of incompetence that exists in some design offices never ceases to amaze me.

me too, it starts at the top and filters down. Try explaining to someone you cant physically make something as there is no access for tooling into a sealed void. when the Boss wants a word with you about for your attitude and behaviour with the full intention of firing your arse.
I like to think managers are like politicians, promise the earth to get you to work for them then find reasons to discredit you and cut your wages with and end goal of getting you to work for nothing. Wont listen wont learn, its obvious why they like yes men, migrants and robots - people who wont answer back or make them look stupid.

[metric_taper]

I was preparing a post on this very topic. What a crazy design feature that was, I wonder how many other lathe models have the same problem. The degree of incompetence that exists in some design offices never ceases to amaze me.

I purchased this lathe new, I was age 20, and was the first tool of this size ever purchased by me. I've learned that "JET" was an importer back in the 70's-80's and my lathe was shown manufactured in Taiwan. I don't know what they were thinking as they must have gotten lathes to copy. When it comes to the tail stock, cross, and compound feed screws, they are all Imperial (as well the main screw). The lathe they copied must have been metric, so they looked at an Imperial tape measure and saw 1/8 inch as the increment vs millimeter, so all four feed screws are 0.125 feed per turn. I can't think of any other reason for this odd screw pitch, I guess it could be worse if they used 7/64" pitch.

[tonyfoale]

I purchased this lathe new, I was age 20, and was the first tool of this size ever purchased by me. I've learned that "JET" was an importer back in the 70's-80's and my lathe was shown manufactured in Taiwan. I don't know what they were thinking as they must have gotten lathes to copy. When it comes to the tail stock, cross, and compound feed screws, they are all Imperial (as well the main screw). The lathe they copied must have been metric, so they looked at an Imperial tape measure and saw 1/8 inch as the increment vs millimeter, so all four feed screws are 0.125 feed per turn. I can't think of any other reason for this odd screw pitch, I guess it could be worse if they used 7/64" pitch.

I was 15/16 when i bought my first lathe, a Myford Super7. I cannot believe that was 60 years ago.
Do not quote me on this but I think that JET and other Asian manufacturers can supply their lathes with either metric or imperial feed screws, depending on the country of destination. Like you my JET has imperial threads but I bought it 11 years ago in the US when I lived there for 3 years. It will not matter soon because I plan on fitting a motor driven ball lead screw. I may even go completely mad and do a full CNC, it would be easy enough.

[tonyfoale]

looks like an impressive mod.
left wondering why you didn't just attach the motor in such a way as to use the existing gear train..

I explained that I wanted a smoother drive, and the whole point of fitting the variable speed motor/VFD combination was to get away from the original drive train.
Also I would not have been able to make the stiffening mods if I kept the original.

[tmoore4748]

Mr. Foale, amazing write-up! I was actually considering a similar modification to a Logan 1875 that I've been restoring, and this might be the impetus to acutally get it done. I've been "restoring" it for over two years now, and every time I walk by it, I'm reminded why the warden calls it my "wall-o-shame." Most of those kinds of projects started ending up at that wall in the shop, and it was the first big one to land there.

Are you able to do any vibration testing, such as with an accelerometer, or a device similar to vibration sensing devices used in the automotive industry to diagnose engine vibrations? If so, I'd really like to see data on how well your modification has performed.

[tonyfoale]

Are you able to do any vibration testing, such as with an accelerometer, or a device similar to vibration sensing devices used in the automotive industry to diagnose engine vibrations? If so, I'd really like to see data on how well your modification has performed.

I could easily put accelerometers in different places but it would not tell me very much because I have not done that with the lathe in its original format. I wish that I had now that you mentioned it.
My warden has no idea what happens in my workshop.

[metric_taper]

I was 15/16 when i bought my first lathe, a Myford Super7. I cannot believe that was 60 years ago.
Do not quote me on this but I think that JET and other Asian manufacturers can supply their lathes with either metric or imperial feed screws, depending on the country of destination. Like you my JET has imperial threads but I bought it 11 years ago in the US when I lived there for 3 years. It will not matter soon because I plan on fitting a motor driven ball lead screw. I may even go completely mad and do a full CNC, it would be easy enough.

The more I think about issues with this lathe, None of the feed dials can be zeroed, as they are part of the hand crank thrust bearing tightening assembly. Thinking back, I've done many improvements on this "pre-assembled kit". Nothing like what you've just done.

The best add on was a DRO back 30 years ago, which cost almost as much as the original purchase price of $1800 in 1977. The price of DROs has come down to where like VFDs they are commodity items. As well making my own backplate and purchasing a new Bison brand 3 jaw chuck.

The spindle thread was a real bastard at 50mm diameter, 8TPI. I recently found 2 backplates on eBay that fit this thread. They were slightly too tight of a thread fit, so I got them centered in a 4 jaw, and retimed the thread so I could use the lathes power feed with an internal threading bar. I manually rotated this assembly to scrape the interference fit. So much for mass manufacturing with interchangeable parts.

[tonyfoale]

The spindle thread was a real bastard at 50mm diameter, 8TPI. I recently found 2 backplates on eBay that fit this thread. They were slightly too tight of a thread fit, so I got them centered in a 4 jaw, and retimed the thread so I could use the lathes power feed with an internal threading bar. I manually rotated this assembly to scrape the interference fit. So much for mass manufacturing with interchangeable parts.

Mine came fitted with an imperial spindle thread but also with a metric thread spindle. I use the imperial thread because the chucks and face plate which came with it fit. To change to the metric one would entail new back plates etc for no benefit. Without going down to measure I do not recall the dimensions. I have an assembly drawing of the complete head and that shows two different part no.s for the spindle labelled metric and imperial. The previous owner bought the second spindle.
I am not a fan of screw on chucks, I much prefer a taper fitting like my old Colchester Student had.

[tmoore4748]

...My warden has no idea what happens in my workshop.

Good gawd, if only. She doesn't understand most of what I try to do, even though I explain. She just sees the pile of uncompleted projects and makes fun of me.