Welding a crankshaft?

[SIR REAL ED]

I confess to being interested in this thread and out of my depth but I've had a though. Could you not buy an M12 stud and cut an M10 thread in one end, or is there not enough metal?

The minor diameter of the thread is the major diameter of the thread minus the thread pitch.  It is any easy way to figure out what minimum size tap drill is needed for a female thread, or what maximum diameter rod you will have when you remove the threads from a bolt.

for example an M6 thread with a 1 mm pitch requires a 5 mm minimum tap drill. Same with standard US threads, tapping a 1/4-20 thread, requires a .200" tap drill (.25"- .05"). 

Inceasing the calculated tap drill size by .1-.2 mm or more is pretty common practice.  Increase even more on larger threads.

As shown below, turning the threads off a M12 bolt with a 1.5mm pitch will give you a 10.5mm rod.

https://www.boltdepot.com/fastener-information/Measuring/Metric-Thread-Pitch.aspx

[n3303j]

https://international.optimas.com/technical-resources/metric-thread-dimensions/
For a 60° thread 75% depth is pretty much the standard.

https://drillsandcutters.com/metric-tap-and-drill-chart/
Metric tap drill size chart.

[Canuck750]

Well after planning on drilling, tapping and fitting a stud I changed course, thought what have I got to loose trying to build up the crank, worst case I just grind off the attempted weld and threading and go with the original plan.

four jaw chuck centered the piece with a dial indicator. Not the easiest piece to secure in the jaws, with the weight on the back of the web three jaws just reach the sides of the flywheel. I trued the face with a dial indicator as well and found the shaft is slightly bent, I can true the tip but the bearing contact surface is then out so I went for the mid length, I don't think I would use this piece given the slight bend (about 15 thousands +/-).

I bet someone went to town with a hammer trying to get the flywheel off after tearing the puller threads out of the rotor.



I welded and turned the extension a couple times, weld imperfections kept showing up until I got it as good as I can



I threaded it with a die, 1st attempt not the best, re-welded it and turned it once again and used a new tap M12 x 1.25. I had turned the stud end to 11.85 mm before placing the die, could not get the die to start at 12.0 mm.



The threads are pretty tight, it would have been better if the threads were lathe cut but I can't seem to figure out the gear box on my lathe, can't get the lead screw operation to reverse, needs some digging into.....

I built up the threads an extra 10mm from the original good crank I have, setting the rotor over the shaft it seemed it could use more length on the threaded end



It will work, just not sure I would use the piece but it was worth the effort

[SIR REAL ED]

Very nice work! Jim(?)

Using a die means you did not have to cut a thread relief at the crank end of the thread.

Interesting that you could not get the die started at 12.0mm, but it worked at 11.85mm.  0.006" smaller diameter for us Yanks.

Always fascinates me what a big difference a few thousands of an inch can make in metal work.

I salute you from afar!   

[Canuck750]

Very nice work! Jim(?)

Using a die means you did not have to cut a thread relief at the crank end of the thread.

Interesting that you could not get the die started at 12.0mm, but it worked at 11.85mm.  0.006" smaller diameter for us Yanks.

Always fascinates me what a big difference a few thousands of an inch can make in metal work.

I salute you from afar!   

Thanks for the kind words!

Jim

[Mike Tashjian]

Playing around with a piece you may not need is a great way to learn by doing.  Using a die to cut full threads is never the best way, so overall that is as good as it gets.  I like to use the lathe to at  least cut most of the new thread and do a final chase with a sharp die if needed.  Reversing the die will get you close to a shoulder.  As with any thread champhering the lead end is a must. When I single point with no place to end I will use a handle on the lathe spindle to hand feed the last partial turn. Or in this case(short thread) maybe even cut the whole thread by turning the spindle by hand.  Did this piece have a center in the large end already?  I have always checked pieces like that between centers and then used a rawhide faced heavy mallet to tweak them back before and after machining.  It was mentioned you lathe may not have metric capabilities so, if doing a job like this again you may opt for a thread your lathe can make.  Then just make a nut fit.  Nice work and pictures. 

[SIR REAL ED]

Thanks for the kind words!

Jim

You are more than welcome Jim. 

I appreciate you (and others here) taking the time and effort to document your practices.  The internet is a great place to learn from the experiences of others, as well as to marvel at human creativity.  You, Charlie, Huzo, Chuck in Indiana and a dozen or so others make Wild Guzzi a valuable, real time tutorial.

I often find myself thinking: "Holy Cow!  That is 50 hours of work to perform, and another 50 hours to document and post!!!"

Another great motorcycle tinkering source is "Some Assembly Required" at ADVRider.com.

Decades of experience in machine/tool design, fabrication, development and testing have led me to REALLY appreciate those who can knuckle down and get things done, and disregard those who turn every repair/fabrication into a NASA/Rocket science experiment endless argument about minutiae.

Everyone who likes to tinker should sit thru a dozen Design Review Board meetings with 5 or more white collar types and an equal number of blue collar/machinists/rednecks.  Amusing, entertaining, and educational all at the same time.

Do you plan to test your repair by installing the flywheel and torquing the nut?

Keep up the good work!!!

[Frenchfrog]

Congrats on having the balls and using the skills to do it !!
You always do such nice work.

[hauto]

use to fear threading on a lathe till I worked in shops that had Hardinge lathes. So painless using a hardinge. Been watching this thread,glad to see you dived in . Just make sure your center is spot on for truing your crank assembled.

[n3303j]

use to fear threading on a lathe till I worked in shops that had Hardinge lathes. So painless using a hardinge. Been watching this thread,glad to see you dived in . Just make sure your center is spot on for truing your crank assembled.

...especially the "Toolmaker" version of the Hardinge. It had a hand cam advanced tool post that allowed you to thread up to a shoulder without a relief groove.
You could get similar results with the old South Bend by running in reverse with the toolbit inverted. But it was nowhere as quick or elegant.

[Chuck in Indiana]

Just a heads up on cutting threads on the lathe. *If* your lathe can run in reverse, you can put the tool in upside down and run the threads toward the tailstock. No pins and needles making sure you stop just in time. 

[John A]

Just a heads up on cutting threads on the lathe. *If* your lathe can run in reverse, you can put the tool in upside down and run the threads toward the tailstock. No pins and needles making sure you stop just in time. 

That’s something I’ve never considered, it’s brilliant in its simplicity.

[cliffrod]

Way to go, Jim- I love it!  Glad to see old parts saved, even if it’s only practice.  Very cool.

Consider this good practice..  when you come to the studio to carve that granite statue you’ve always wanted to carve, just remember that when you cut stone, you will only get one chance to do it right..

[Moparnut72]

There is a gal Blondihacks who does lathe machining on tube. She has one covering machining threads in which she covers doing them in reverse to prevent a crash. She is an excellent teacher mainly covering the basics especially for noobies like me. Even experienced operators have good things to say about her. I will try to find the video and post a link.
kk
Edit: Here's the link.             https://youtu.be/q7scadYptTI

[Canuck750]

There is a gal Blondihacks who does lathe machining on tube. She has one covering machining threads in which she covers doing them in reverse to prevent a crash. She is an excellent teacher mainly covering the basics especially for noobies like me. Even experienced operators have good things to say about her. I will try to find the video and post a link.
kk
Edit: Here's the link.             https://youtu.be/q7scadYptTI

Blondihacks is great, I subscribe to her Youtube!

I have not been able to get my carriage drive to reverse and the cross slide power drive never did work since I bought the used lathe years ago. I decided after this die threading exercise its time to get into the lathe and see what's up and fix the thing. I got a bunch of the lathe stripped today and it looks like the gear box is the source of the longitude travel issue, a very ugly gear, hopefully I can find a replacement.

broken teeth, not pretty

taking a screen shot

My lathe is the same as a Grizzly 10" x 36" gear head lathe (many different name tags on this lathe by various distributors).

I haven't got into the carriage yet to see why the cross slide drive is not engaging.

Always something to fix, I wanted to clean up the lathe anyways so this is as good a time as any.

print screen windows

[Huzo]

Just a heads up on cutting threads on the lathe. *If* your lathe can run in reverse, you can put the tool in upside down and run the threads toward the tailstock. No pins and needles making sure you stop just in time. 

Yes you can Chuck as I’m sure you have, but you need a damn solid cross slide to do so, because the force is lifting the slide instead of pushing down on the bed.
But nothing ventured, nothing gained. 

[Huzo]

Well after planning on drilling, tapping and fitting a stud I changed course, thought what have I got to loose trying to build up the crank, worst case I just grind off the attempted weld and threading and go with the original plan.

four jaw chuck centered the piece with a dial indicator. Not the easiest piece to secure in the jaws, with the weight on the back of the web three jaws just reach the sides of the flywheel. I trued the face with a dial indicator as well and found the shaft is slightly bent, I can true the tip but the bearing contact surface is then out so I went for the mid length, I don't think I would use this piece given the slight bend (about 15 thousands +/-).

I bet someone went to town with a hammer trying to get the flywheel off after tearing the puller threads out of the rotor.



I welded and turned the extension a couple times, weld imperfections kept showing up until I got it as good as I can



I threaded it with a die, 1st attempt not the best, re-welded it and turned it once again and used a new tap M12 x 1.25. I had turned the stud end to 11.85 mm before placing the die, could not get the die to start at 12.0 mm.



The threads are pretty tight, it would have been better if the threads were lathe cut but I can't seem to figure out the gear box on my lathe, can't get the lead screw operation to reverse, needs some digging into.....

I built up the threads an extra 10mm from the original good crank I have, setting the rotor over the shaft it seemed it could use more length on the threaded end



It will work, just not sure I would use the piece but it was worth the effort

Is the leadscrew on your lathe metric Jim ?

[Moparnut72]

Yes you can Chuck as I’m sure you have, but you need a damn solid cross slide to do so, because the force is lifting the slide instead of pushing down on the bed.
But nothing ventured, nothing gained. 

Blondihacks added that doing this can be hard on the lathe. She also said that some SAE lathes can do metric threads with the addition of a 39 tooth gear.
kk

[huub]

i've got a 127 tooth gear for the carriage drive  of the lathe if i want to do inch sized threads , and a 120 tooth gear for metric.
should work the other way round if you have a SAE spindle on your lathe

[Mike Tashjian]

The instructions for many lathes include threading details. That would include gear changes for imperial and metric threading if your machine is capable.  I never see anything about reversing the carriage for threading, just release the half nut and move it back and watch your thread dial for reengaging.  That gear appears to have been damaged by someone trying to engage it under power.   Sourcing a new one should be fairly easy once you identify it's specs. Or make one using your lathe and mill. That is what I do when one is not easily sourced.   

[Canuck750]

The instructions for many lathes include threading details. That would include gear changes for imperial and metric threading if your machine is capable.  I never see anything about reversing the carriage for threading, just release the half nut and move it back and watch your thread dial for reengaging.  That gear appears to have been damaged by someone trying to engage it under power.   Sourcing a new one should be fairly easy once you identify it's specs. Or make one using your lathe and mill. That is what I do when one is not easily sourced.   

Thanks Mike,

I got the gear box tore down, four gears needed, lucky Grizzly has them all in stock. I know why the left hand feed position pin would not budge







the power cross slide does not work because the gear on the cross slide lead screw is missing!, again in stock at Grizzly. Why would anyone have removed the gear in the first place ??

This lathe comes with change gears that are swapped for the various metric pitches and then the positions of the quick change gear box are set to the corresponding pitch chart. On my old Myford ML7 if I cut a metric thread change gear swaps were required and I had to stop the lathe and reverse it, could not release the 1/2 nuts as the manual said the thread indicator could only be used for imperial threading. With this Chinese lathe I don't know if that applies, supposedly I could just try backing off the lathe and follow the thread indicator dial to re-engage the 1/2 nuts, that would be nice.

My lathe is a Grizzly is a G400 3G - 12" x 36" Model, anyone know if these are built as metric or imperial machines? not hat I would know what the difference is or why it matters.

[Huzo]

Hmmmm…
You can tell a lot about a bloke by his fingernails.

[Muzz]

I take my hat off to you Jim. If I ever learn half of what you have forgotten I would be a happy man.

Those teeth have had some "abuse". Power fed the toolpost into the headstock?

[Canuck750]

Hmmmm…
You can tell a lot about a bloke by his fingernails.

You can tell I can be careless swinging a hammer! My split in half index finger nail has finally grown out, I slipped with a long punch, guess how much that hurt when the punch met the finger. Think dropping to floor.

[balvenie]

You can tell I can be careless swinging a hammer! My split in half index finger nail has finally grown out, I slipped with a long punch, guess how much that hurt when the punch met the finger. Think dropping to floor.

Did I ever tell this forum about the time that I clouted a finger with a heavy hammer? I made it inside, turned on a ceiling fan Flat Out and lay under it on the tiled floor, for a Long Time. Thanks for reminding me Jim I'm ok now and can talk openly about it but I do know how those things can weaken a bloke. Sorry to hijack. It was compulsive. Hey, maybe I'm not ok after all