Viceroy T.D.S 1/1 G.B - 3MT Morse Taper Spindle Adaptor

[dazz]

I decided to make a Morse Taper Spindle. It just looked like a good exercise in turning to produce what might be a useful tool.

I don't have any driver dogs, so I tapped a bolt into the side of the bar. My dead center is quite long so I used a wooden spacer bolted to the driver plate. The two bolts were then wired together. Initially I didn't bother balancing the weight, but I quickly found the vibration was too high. I used three bolts and a piece of plywood to counterbalance the driver plate.

The morse taper was produced using the top slide (rather than my taper turning attachment). Setting the angle accurately was essential. I wanted to complete all turning without moving or removing the work. There was no possibility of testing the fit because of the cutting order I had chosen. I had to get it perfectly right, or accept sub-standard results. I held my parallel bar between centers and used a dial gauge on the top slide to set the correct angle. A No.3 Morse Taper is 19.922:1. This corresponds to 2.541mm/4" read from the dial gauge (I have a mix of metric and imperial tools). Getting the top-slide to precisely this angle took a while but it was worth the effort.

I then hogged out the basic shape of the taper spindle. I parallel cut the fat end of the taper to 23.950mm, the maximum diameter of the MT3. This made it easy to axially locate the position of the taper along the length of bar. I turned the taper to final size.

Turning progressed towards the tailstock and I finished the body and register. The nominal diameter of the register is 1.5" but the register on my lathe spindle is .0005" less than that (1.4995"). I decided to aim for the mid point and cut to 1.4997". I was able to achieve this accuracy because I still had the top slide set to the taper angle. For the final cuts, I calculated how far the top slide needed to move towards the chuck to achieve the depth of cut I was aiming for. It worked.

The next challenge was the spindle thread. I haven't cut a thread anything like this size before and I figured that this part had the most potential to turn my work into scrap metal. As far as I can see, the thread is the primary method of locating the chuck. Any error in the thread will result in run-out errors. I needed an accurately ground thread cutting tool, so I made my tool cutting jig. This worked very well and provided accurate angles and straight cutting edges. When bevelling the end of the bar, it cut broad tight text-book clock spring chips. No sign of chatter, and a good finish.

The thread cutting tool needed a round nose. I used a piece of light sheet steel (roofing sample) and drilled a 0.9mm hole, then filed away enough to leave a radius template. I then hand ground the nose of the tool to fit the remainder of the hole.

I cut a groove for the cutting tool to finish in at the end of a pass.

I cut the thread depth and profile to match the measurements of the lathe spindle making an exact copy. I don't have a go/no-go thread gauge for the spindle so trial fitting to a chuck might not have ensured that the thread was in spec and would fit all chucks. Unlike the morse taper, I could not find a spec for the thread, so I made an accurate copy of the lathe spindle thread.

Once the thread was cut, it was time to remove the work from the lathe for the first time and try it for fit. The thread screwed into the three-jaw chuck with a good fit, but the spindle disappointingly stopped when it reached the cylindrical part of the register. After an initial burst of four-letter anglo-saxon expletives, I realised what caused the problem. The process of cutting the groove for thread tool clearance had raised a slight burr on the register. It wasn't even visible, but cutting a miniscule chamfer was enough to remove the obstruction. The threaded end and register then fitted perfectly.

The next stage was to cut away the thin end of the morse taper. Only then could I try it for size in the tailstock socket. It fitted.

All that was left to do was to drill, then bore out the spindle nose. It all went smoothly. That completed the job. The only thing missing is something to allow a spanner to be used to unscrew the spindle. That will have to wait a while. I don't have a mill.

The success of this job depended entirely on the accurate measurement of both the original spindle, and the copy. The cutting sequence allowed the spindle to be made without moving it to ensure maximum accuracy. The down side is that trial fittings were not possible for the taper. There was just no room for error. The proven accuracy of the lathe and high quality measuring instruments made it possible to achieve tolerances measured in 1/10 thou".


I now have a potentially useful accessory to add to my meagre collection of tools. I say potentially because I didn't make this for any particular project I have in mind. I think it will only become useful when I need or make some non-standard attachment to be held in the tailstock.

It's been an interesting exercise in precision machining. It was challenging (stressful) because of the many potential opportunities for a single mistake to wreck the job. Fortunately, it all went to plan. I can safely say that this project turned out exactly as intended.

[dazz]

The drawings are attached in a zip file. The file contains two drawings. One of the 3MT spindle adaptor design, and one of the lathe spindle measurements.

[dazz]

Just a picture showing the use of the parallel bar and a dial gauge to set the correct angle on the top slide.

Moving the top slide exactly 4" will measure 2.541mm on the dial gauge when the angle is correct for a morse taper No.3.

Different morse taper sizes have slightly different tapers.

[preston]

Daz,
Just a note to congratulate you on your workmanship. machining the taper and thread without being able to test fit them was a real test of skill.
Thanks for your postings on the Denford overhaul. I bought a metric version of your lathe at the beginning of this year, and your information has been most helpful in getting it set up.
I've just finished a collet chuck for ER32 collets for my lathe, and it works well with very good accuracy (as described in Model Engineers Workshop).
Its nice to see you are getting such good results with the lathe after all the overhauling work you did before.

Regards, John.

[dazz]

Hi

I am happy to hear that you have found something useful in my ramblings.

I would like to have a go at making the MEW collet chuck but the fatal flaw with that plan is that my lathe is imperial. I'd prefer to buy the nut and make the rest of the chuck to fit a spare back plate I have. I can't cut the metric thread pitch to match the nut. I know I could buy the right gears to do the conversion to metric, but the prices are beyond reason.

I think I could make the nut, but not necessarily from a suitably hard wearing grade of steel. I have a list of other projects I want to complete before I will be considering doing a collet chuck.

Why don't you post some pictures of your lathe and work?