Makeshift repairs and babbit

[scott p]

Yes a copper pipe would be ok with me if I can find one. The old bush is fairly thick, perhaps I could bore the old bushing out and push a copper liner in.

The wrist pin has any where from 1/2 to one thou wear, measures 7/8 in and is very hard.

I took the old bushing out and set the rod on a granite plate. The rod little bore does not seem to line up to the big bore. I need to check that out. If babbit does in fact swell as it cools I could try filling the small end and then somehow drilling and reaming to align with the big end.

 The small end bore is roughly tapered by about three to four thou . By design or just loose tolerances?
I jumped the gun on the bushing I made and did not discover the taper until too late.

The old bush is not tapered and appears to be soft steel with bronze or some fairly hard liner. Possibly I could bore it a little and  pour babbit or tin solder  and ream it.

Oh well, I will be thinking about it.

[cobbadog]

Are you certain that the taper should be there? I haven't come across that design before. It has always been a parallel fit with either circlips or even a lead plug hit into place to keep it there. Even if the fit was a bit firm in the piston to help hold it.

[38ac]

So 38ac glad to hear some one has been there done that. What would be your procedure for making a bushing to fit the small end of the con rod ?

For Bamford Z2 and any other small ends I turn a piece of brass with the OD being size to size with the bore, this gives a press fit. The ID is drilled undersize while in the lathe. After pressing it in the rod it goes to the mill where a correct size mandrel  for the big end is clamped on the table. The is holds the rod  in proper alignment to bore and finish the small end bushing once the center is located.

[scott p]

Sorry about that, I didn't mean to imply that I thought it was a factory taper. It was basiclly a question and you answered

it. Highly unlikely, even for some kind of alignment problem.

Also, the actual measurements of the bore were all over the place to some degree and averaged out as a taper.

38ac's explanation of fitting and sizing a bush is good news. I think if I make  mandrels about say three or four inches long

for both bores I should be able to easily determine if the bores are  parallel to each other. If needed I can use his

technique to bring things together.

Did I read somewhere a long time ago that a hone will have a tendency to straighten things out in a bore ?

[38ac]

I am sure that the more creative and skilled people could fit a bushing with basic hand tools but I am not one of them, LOL. I measure the ID of the big end of the rod. Then turn the mandrel to size and square the ends that way I can just clamp it on the mill table. If doing this on a Bridgeport type mill it is imperative that the head is trammed in square to the table.  The pin  clearance for  the small end is best described as small  as you can make it and still push the pin through with your fingers. I don't own the Sunnen honeing machine I should own to fit the pin. I get as close as I can with a boring head and finish with an ordinary brake cylinder hone.

[cobbadog]

Is all good, sometimes we can read things and mis-interpret them, I'm guilty of that a lot.

Something that may help you out is to go to YouTube and type in what you want to do. You will be amazed at how many videos are out there on every topic you can think of. I am about to retire and only about 18 months ago I bought a cheap Chinesium metal lathe 2nd hand. I have then watched many videos and started to buy more tooling and even had to make my own thread chasing dial because my lather has a metric lead screw and I need to make BSF and BSW threads. Yes, I could stop the lathe and reverse it but this has no brake on it so damage would happen. My research paid off and now have a dial perfect for the job.
So have a look and see some options that might help you out with the tools you have.

[38ac]

I would be interested in how you make your thread dial work as it has always been my understanding that if one released the half nuts that the dial can only be right after 127 revolutions when threading metric on an imperial lathe or vise versa.  As you may know there is  no mechanical way (gearing) to EXACTLY convert an imperial lathe to a metric one, the math equation goes to infinity, much like pie, 3.14,,,,,,,,,,,,, the 127 ratio used for lathe conversation gets things close enough for most work but in an exact world a lathe can only thread one or the other without changing the lead screw. 
I am not downplaying what you have done! I like to replicate it if I can.  I thread a lot of metric stuff on my imperial lathe and have always backed it up but I have a clutched headstock which makes it quite a bit easier to accomplish.
 

[cobbadog]

Hi 38c,
My Chinesium lathe runs a 20mm lead screw. I have all the gears for the head to change the TPI as per the chart on the lathe itself. As you must be aware the big issue is to be able to engage the half nuts at the same position each time as you make your pass a bit deeper each time. This is where I came up with some help on a machine shop form on the Smokstack Forum and for the BSW and BSF threads I required 2 different size gers to mesh onto the lead screw.
 
I haven't got those numbers here tonight but I can go out to the shed tomorrow and take some pics and show you what I made and as basic as it looks, it works. I also bought a booklet which also had a lot of information for general machining work and some of it goes right over my head as I am not a machinist by any means and only a beginner at best with a lot to learn and willing to do so.

Let me know if you wish to see what I made and use.

[38ac]

Yes, I understand what you are doing. My big lathe is a Colchester copy and Imperial,  my smaller lathe is Chinese but also Imperial but both work the same way. Mine are equipped with Norton boxes so I don't have to change gears, just flip levers but it accomplishes same end. Places a 127-1 ratio in the lead screw to allow metric threading. Also have threading dials but they are worthless when threading metric. They won't put me back on the lead. Now it is my understanding that using a metric lathe adapted to imperial that the same thing happens? Makes sense but also can be wrong. There may be some new techniques out there but old school taught one to leave the half nuts in and back 'er up.

[cobbadog]

Yes, exactly, leave the half nuts engaged and reverse and that is fine IF your lathe has a brake and will stop as soon as you hit the stop button but mine runs on so If I was running a thread up a shank to the head of a bolt I would crash into the head of the bolt.

[scott p]

My mill is not marked but looks like a jet type with a round column that will  swing around  and the tram is, I suppose, fixed. There are no marks to tell me when I am straight out with the deck. Bought used with lots of tooling.

I should check the tram before I do anything about this small bore project. I made up a mandrel for the big end but this is turning out to be too time consuming, needs to be a winter project.

I have a south-bend garage sale lathe with lots of tooling. I consider the thread dial indicator to be a form of magic. One mark for even threads and another mark for odd threads. Metric a whole different story, indicator with several different gears.

Cobbadog, are you going to post what you did to build a indicator ??

[cobbadog]

Sure will as soon as time allows. we have been away on holidays and now my work is bombing me with way too much. Would love some time to take a breath. As soon as I can I will do for you.

[cobbadog]

Ok I dug this out of the file and hope it shows you how I built it. It shows 3 gears that I bought off a Chinaman and the product was brilliant and cheap off Fleabay auction site. I welded the round pieces at right angles and use the single bolt as a pivot and a lock to hold the dial indicator onto the lead screw. I also made the marks on the top of the indicator and used a white marker pen. The theory was after I worked out which size gears I needed and I will post a copy of the info I found, I then put the indicator in the hole and used the grub screw to hold the gear on the end of the shaft. So far this has worked well for me to make some BSF threads using a 20mm lead screw.

THREAD CHASING DIAL INFO

I have 3 gears on the stem of my metric thread cutting dial and they are 28, 30 and 32 teeth. Those give you the prime numbers 2,3,5 & 7, which combined with a few different gears will give you all the metric thread pitches you will need. Not quite as straightforward as cutting TPI on an imperial lathe, but 95% of the world's machinists cope. I can take a photo of my thread chasing chart, ie dial teeth v pitch, if that will help.

So that means I would need a 20, 21 and 27 Tooth gear to get all the thread pitches my lathe allows for....


The screw-cutting thread indicator dial meshes with the leadscrew via a 30 tooth gear. To get the indicator dial to rotate once the carriage has to move 90mm (number of teeth x leadscrew pitch). Only those metric pitches that divide exactly into 90 will be able to use the dial when screw-cutting. Thus pitches of:-
0.5, 0.6, 1.0, 1.25, 1.5, 2.0, 2.5 and 3 will work, pitches of 0.7, 0.8 and 1.75 won′t work.
Replacing the 30 tooth gear with a 28 tooth gear would work for the missing pitches but not for all. With a 28 tooth gear the carriage has to move 84mm for a full turn of the indicator and 84 is divisible by 0.7, 0.8, and 1.75. So either change the gear, make an indicator that has both gears or just leave the leadscrew engaged and reverse the lathe.


I think on my leadscrew a 21 tooth gear on the dial indicator will get me the missing pitches. 21 * 3 = 63mm per full turn
For 0.45 pitch: 63 / 0.45 = 140.
For 0.7 pitch: 63 / 0.7 = 90.
For 1.75 pitch: 63 / 1.75 = 36.
Therefore a 21 tooth gear will give these pitches on a full turn and half turn. It will give the 1.75 and 0.45 on each quarter segment.
So I guess I need to source a 21 tooth gear.

With a 3mm pitch lead screw, you do not need a threading dial for the 1mm and 1.5mm threads. They will be synchronized at any place that you engage the half nuts. You literally can not get them wrong unless you remove and remount either the tool or the work.

I have not worked with a lathe with a metric screw, but I believe they usually have thread dials with some internal gearing. This is one of the things that proponents of the metric system do not talk about when they are bashing the English system which uses threads defined in threads PER inch and therefore has much simpler threading rules. I can attempt to give you some guidance for a simple dial that would work but may not be as convenient to use as the ones usually provided by the OEMs. The suggestions below assume a simple dial with the gear and the dial on the same shaft with no additional gearing between them.

The 1.25mm thread will synchronize at multiples of 5mm (1.25mm x 4 = 5mm) that are evenly divisible by 3mm. So you would need a gear that would allow you to travel one of those distances (15mm, 30mm, etc.) The obvious one seems to be 15mm and you would get that with a 5 tooth gear. That's too small. 10 teeth would give you a 30mm distance and that may be workable. If you have an even number of divisions on the dial face, you would be able to engage the half nuts on two of those lines that are 180 degrees apart as they would represent distances of 15mm.

Likewise the 1.75mm thread will synchronize at intervals of 7mm (1.75mm x 4 = 7mm) that are evenly divisible by 3mm. A 7 tooth gear would provide a 21mm distance (3 x 7mm) but I don't know if that would be practical. You may have to go to 14 teeth for a distance of 42mm. With 14 teeth for a distance of 42mm, if you have an even number of divisions on the dial face, you would be able to engage at two of them that are 180 degrees apart. So the same dial would work for both of the threads that you mention that actually need a threading dial.

You can work out other gears for additional thread pitches in a similar manner.

If you use these suggested gears you will have to wait a bit for the synchronization points. It may be faster to just leave the half nuts engaged and back up the spindle. That will work for all threads.

I would appreciate it if someone can check my logic and figures above.

[38ac]

Wow, a lot of thought went into that. Thanks.
  Even though my lathes have clutched head stocks and a brake it is near impossible to stop close to a shoulder when you cannot disengage the half nuts. Another technique is to mount the tool upside down or on the back side of the spindle. You then cut a small relief groove up next to the shoulder (no different than you end up with when using the half nuts to stop the carriage) and cut the thread from the shoulder out running the spindle backwards leaving the half nuts in. Aligning the next pass is accomplished by turning the spindle by hand once you are close bumping the switch.

All in all of I had to cut many metric threads I would find a metric lathe😊

[cobbadog]

Doi ng all the sums with help I must add really did my head in but I got there in the end. Even now just briefly reading the memo I wrote out I started having a migrain and all the pain came flooding back and I too wonder how this all worked out.
I received so much help in working this out from another Forum I visit and that is Smokstack and it is based in the USA and has so many topics it will make your head spin. In the machine shop section which covers nearly all types of lathes, mills shapers drills etc and the guys there are always polite and very helpful. I have had a lot of help from these guys in making improvements on my lathe. Things I never knew about like centering the tailstock and for this I bought a dial indicator that measures down to 0.001mm w2hich for me is accurate. When applying the information on how to centre it I did get it to  being 0.000mm, perfect by the dial and I am certain that the final adjustment was more about the grunt I made rather than the adjustment of the screws.