Jones and Shipman 540P Rebuild (Round 2)

[AndyPandy64]

First - That's one hell of a thread for your first !! - Since you admit that you are new to threads, I presume that you may not even know the correct flank angle of an ACME thread -- this may also be why you think that you omitted to consider 'Tool wear'. To measure the wear after cutting a single thread in Bronze, would be difficult even with the most sophisticated inspection equipment, so I suggest that you have cut it too deep or not at 29°

There's nothing unusual about an OD of 3/4" - though that Dia. would normally be a 6tpi ACME - as it happens ACME threads are very much designed to transmit power, and 2 start more so, therefore all the 'standards' go out of the window.

What dia. did you machine the 'bore' to? And how deep did you make the final cut? - - - For a full depth thread the bore should have been ~ 0.55" and the thread depth 0.1" but since it is two start, you should have also taken note of the Helix Angle when selecting the tool. With a 5tpi Lead and 0.75" OD the helix angle is close to a massive 11° 5' so if you were using a 'standard' ACME Thread Chaser the clearance should have been modified - there would have been 'rubbing' on the flank which would affect the thread form - potentially causing the poor fit.

Thanks J-G. I think you have identified my problem. Helix/clearance angle

The shaft OD is 7/8 but everything about the thread is ACME 5tpi. Tool geometry, apparent pitch, DoC, etc. ie 0.110 DoC. Just its a two-start thread

I got all the data from the Machinist Handbook

My plan was to first cut the internal thread to fit the ends of the existing lead screw where the threads are not worn. Then cut the thread on the new lead screw to fit the new nut. So going by the book was not strictly required. I hoped this would allow for my complete lack of experience

I thought I'd factored everything in, including an undocumented way of cutting two-start threads on my 1800

But I had not considered the helix angle. I've just checked the tool I ground and whilst it fits perfectly on the 1x5tpi test thread, it does rub on the two-start 2.5tpi thread. I've just put the test single start 5tpi next to the original screw and the difference in helix angle is so obvious. 5tpi helix angle is about 5° against the helix angle on the two-start is about 10°

Not a problem for the internal thread since I was using old J&S boring bar which takes a 1/8 (maybe bigger, but min size for a 5tpi AMCE thread) HSS which I ground. I think the helix/clearance angle did not matter because the tool size was so small. But for the external I ground a 3/8 HSS blank and I’ve just checked and the clearance angle is about 6°

Your explanation helped a lot. Time to make another one I think

This time I might also be brave enough to drill the 3.5” deep ¼” oil hole in the end !!!

 

[J-G]

Good - at least my input seems to have been useful. I have written a program (under Windows) to calculate the various dimensions of many Thread Forms, inc. ACME & Trapizoidal, which you may like - send me a PM if you are interested.

At 7/8" Ø the Helix angle on a 2 start 0.2" pitch is 9° 19' 47" - single start would be 4° 41' 46".

The DoC for the external thread should be 0.105". If you have the top-slide set over at 14½° the total travel should be 0.108". It's quite a challenge to measure the root Ø but if you can devise a method that should be 0.665". Internal threads are not generally full depth - the OD has to be correct (or marginally oversize) - but the root is usually larger than 'Nominal'.

The most important dimension is the Effective Ø which ( for a Class 2G fit) is 0.7693". Measuring that is probably more complex that you yet appreciate. The best way is the Three Wire method - which is what my program is designed for. Over 0.1" 'wires', the mic reading should be between 0.8876" and 0.8929" (2G fit).

The pragmatic approach (make the nut to fit the existing first) may well be your best course of action but considering the type of machine that you are refurbishing it might be prudent to strive for the highest accuracy and to make the new lead-screw first and make the nut fit that.

 

[deema]

I hadn’t finished working on the grinder, I had been stumped by how to get the main spindle motor out. It’s buried in the bottom, and the attachment system is deep inside the almost inaccessible column. Coupled with this, the whole thing was covered in a deep layer of grinding dust and hydraulic fluid. Any attempt to look / feel how it was attached resulted in coming out like I’d been down a very unpleasant coal mine.

Them a stroke of luck, I happened across the parts manual for the earlier version of my grinder. This uses photos of the parts rather than drawings, and the motor system was actually shown in its fullest extent.

The first diagram is what is in the parts manual for my iteration of the machine. Not much detail to go on.

This is from the earlier parts manual, and it shows the whole system. The motor isn’t detached from the mounting plate, the whole plate with motor comes out By removing the pulley and then removing the four bolts, Z3206/28, and /10 Simple!

 

[deema]

The pulley in my machine is locked in place by a bolt you access through a cut out within the pulley. Not the best access. You can just see it through the upper slot. The photo is taken after literally scrapping off abiut two large handfuls of gunk to reveal the system to tighten the belt.

The lower retaining plate is held on by two bolts, in the photo this has been removed leaving just the upper bolts of the belt tensioner to be extracted. @Sideways was on the other side ready to catch the motor when it was released.

 

[deema]

The motor is attached to a plate that is in its turn attached to another via four anti vibration mounts. For precision grinding any vibration will be seen in the finished part.
Have I said everything is covered in a thick coating of grinding dust and hydraulic oil? Well the photos are after scrapping most of it off, but before clean up.

Someone had been here before me and marked the top of the mounting arrangement.

With the first plate removed you can just see the remaining anti vibration mounts.

I don’t have a parts washer……but a Yorkshire version……think penny pinching cheapest solution. I use diesel as my preferred degreaser. However, I absolutely hate cleaning up thick oily stuff, I need a lot of motivation to do it. I just wish I could think of a quick way of doing it. A proper parts washer would be a start, but the stuff coming off is so thick that I think it would block up the pump very quickly. Anyway. The parts had an initial wash and were left in the diesel over night to soften the remaining gunk.

Today, I have to change the stretch limos brakes (long wheel base van) so probably not get anything done on the grinder. Any excuse not to carry in cleaning up the bits!

 

[Tonks4x4]

I have also recently purchased one of these and it’s a little tired. My spindle is a bit squealy so needs some investigation. Great thread so far keep it up…

 

[wallace]

I quite like cleaning parts, I find it cathartic. A proper parts washer would be nice though

 

[deema]

The next bit to come off is the last remaining motor which provides power for the head rise and fall, the power rise and fall is an option on this machine, the standard machine in just manual. After winding the head up and down manually I can say that if you’re thinking of one of these machines get one with the power head option……it takes a lot of winding otherwise!

Firstly the assembly drawing from the parts manual…..right, that helped a lot!

The motor is held in by an intermediary plate between its B14 mount and the actual mechanism. The intermediate plate had 3 cap head screws that hold it on. All can be accessed without stripping the whole mechanism off the machine. Weirdly they were imperial! I wasn’t sure if the cavity it reveals would be oil filled…..it isn’t. There is a dog drive that connects the motor to the shaft, the other dog is shown when looking inside the receptor from where the motor was removed. A key also links the two parts…..I found the key in the bottom it had escaped….how I’ve no idea how!

 

[deema]

The motor bearings were badly worn, a nice grinding and scraping sound could be heard as the shaft was turned. The whole motor was covered in ***** The cooling fan when cleaned was actually clear plastic! I’m really glad a took the time to clean this motor up.

 

[deema]

The lack of a key had caused the dog to spin on the shaft, it was also held by a grub screw that had dug a nice groove around the motor shaft end.

 

[deema]

Today the gods didn’t smile on me. Removing the dog from the end of the shaft required a lot…..I mean a lot of pressure from my press. The bell end plate of the motor is aluminium and can’t stand much pressure, so I carefully ensured it was supported….at least I thought I did.

Yep, I broke it…..bother!

 

[deema]

You can usually get replacement parts for motors, a B14 motor bell end is usually about £10…..however this motor is long since out of manufacture

At least it’s a standard motor, 0.18KW 4 pole 63 frame size. I can buy one easily….just a few more pennies! Not going to shed too many tears, the shaft would have needed a bit of TLC to machine a sleeve to repair it If it hadn’t broken.

 

[deema]

More cleaning!

The top spindle pulley is held on my a nut and it’s pressed onto a tapered shaft. Not a big deal, as it’s the same nut as that which holds on the grinding wheel and the same tool will remove it. The pulley is threaded and again, the grinding wheel puller will also pull of the pulley.

 

[deema]

The column rise and fall is driven off an Acme threaded bar. After revealing it from under the grime I was pleased to f8md that it didn’t appear to have any significant wear. Still more cleaning required if those threads!

 

[Ollie78]

Pretty fascinating thread as usual deema.
Will we be able to send you our handplanes to have the soles ground to sub micron tolerances ?

Ollie

 

[kaiten]

Hi @deema,
as indicated int the 540 valve block thread, I am also rebuilding a 540. I am currently reassembling the wheelhead carrier into the wheelhead column, lowering it onto the Z screw. I am scratching my head on the safety nut orientation (part G12639/imperial, G13174/metric=mine). It is a relieved nut and it has to be grabbed somehow by the N16662 catch finger we see on your nice shot just above this post. I still do not get exactly how it is supposed to work, but the orientation I found mine upon disassembly seems to contradict the parts lists schematics / pictures. Could you check yours or dig out a macro shot of the safety nut in the normal position ?

thanks a zillion,

 

[deema]

The safety nut is just to stop the column falling right down when the bronze nut is worn out. It should be a loosely goose fit, and just follows the column. Next time I’m in the workshop I will post a photo of it.
You want a little gap between the nut and the rest of the carrier so that when the bronze nut fails, on the operators daily oil of ‘F‘ they will notice the gap has disappeared…….like that ever happened!!

 

[kaiten]

Hi @deema, and thanks for this very responsive answer. I now realize my safety nut understanding was way out in terms of potential situation it was made to adress: I figured it was made to ensure the nut and swcrew stayed perfectly aligned when the end of the screw leaves the nut on the extreme end of the top travel. Your explanation makes more sense indeed !
Thanks!

 

[deema]

@kaiten sorry it’s taken so long, today was the first time back in the workshop. Hope the photo helps, I’ve yet to clean the system!

 

[deema]

The new replacement motor arrived so I was able to assemble the dog back onto it and also attach the flange interface plate. The motor is a diddy 0.18KW. This is a sealed TEC motor. The foot mounting will be taken off before it’s out back.