270 Offy

[mayhugh1]

The two lathe tools shown in one of the photos in my previous post were used to turn the crankshaft journals. Both of them use sharp carbide grooving inserts that were shop modified. The gold colored insert is .120" wide, and in order to reduce chatter its center was notched out. The outer sides of the insert and the insides of the notch were relieved with a diamond burr to allow shallow side-to-side turning. After relieving the insert, its holder had to be ground down to avoid rubbing on the workpiece. At 80 rpm, this tool was capable of turning the main journals to a predictable diameter with a smooth surface finish using a d.o.c. of .010" (dia). Unfortunately, the holder wasn't stiff enough to work as well on the rod journals which required more stick out.

The rod journals were turned using the black .204" wide insert. The stock insert already had relieved outer sides, and so relief had only to be added to the insides of the notch. This insert was also capable of acceptable surface finishes, but its huge contact patch even with the added notch combined with the flex in the system to make actual d.o.c.'s somewhat inconsistent. Turning all four journals to a common diameter was hit and miss, and when I had somehow managed to get all four journals to within a thousandth of .537" I stopped. The TIR's all wound up slightly less than a thousandth.

The rod journals were finished in .008" d.o.c. (dia) steps, and the TIR and diameter of each was checked after every pass. The technique that gave the best results was to start the turning operation in the center of the journal and then power feed to its leftmost side and stop. After reversing the feed direction, the cutter was power fed to the rightmost side. The feed direction was reversed again and the cutter once more power fed to the leftmost side. Because of space limitations, the journals could only be mic'd in their very center, and so it was important to not leave behind a narrow and difficult to detect ridge in the center of the journal. All operations were performed with the lathe in back gear and set to 80 rpm, and so the process was pretty time consuming. The journals were finally polished at 400 rpm using 600g paper.

Earlier, when roughed out on the mill, excess stock was also left on the webs on either side of the journals. This was removed next using a pair of repurposed boring bars. At this point, the offset turning operations were complete with (hopefully) no further need for the offset center-drills. The close-fitting rod journal spacers will remain in position until the crankshaft is completed. I didn't see any change in any of the TIR's that I continually measured during the rod journal turning operations.

The workpiece was re-installed in the lathe with the crankshaft's main axis between centers. With some care in positioning the drive dog and adjusting the tailstock pressure, I was able to get the main journal TIR's matched to the values measured before and after the rod journal turning operations. Even with the rod journal spacers in place, however, it was possible to more than double the runout with too much tailstock force. The excess web material left on either side of the main journals was removed next.

The workpiece was returned to the mill where the rear (ball) bearing and flywheel retaining surfaces were hexagonally roughed. It was then returned to the lathe so these areas could be semi-finished with a conventional turning tool. Again, all the TIR's remained consistent with those previously measured.

The workpiece was returned to the mill where the front (ball) bearing surface was roughed in. The Offy crankshaft has a skinny extended nose that will eventually receive a Loctite'd drive gear and a hardened nose for the starter clutch. This troublesome section will weaken the workpiece and likely create problems for the main journal finishing operations, and so this portion was left for later.

After returning to the lathe, the front (ball) bearing surface was semi-finished. At this point none of the TIR's had changed since that mysterious overnight movement after the initial main journal semi-finishing step. I began final finishing the main journals with the front (ball) bearing journal which went perfectly. However, after finishing the center journal, I found its TIR had ballooned to .004" - likely due to workpiece flex.

After grinding a razor sharp HSS tool and indicating it in the toolpost, I was able to scrape away most of the runout by manually rocking the spindle back and forth over the journal's high spot. With no way of putting material back though, I ended up with a .005" undersized journal. The results were essentially the same with the other two journals even with the HSS tool.

I roughed in the two ends of the crankshaft so it could be trial fitted in the crankcase lower half without the front and rear ball bearings. The fit wasn't as sloppy as I expected, probably because the three TIRs aren't lined up with respect to one another. In any event it will become worse as the engine is run and the bronze bearings become 'wallowed' out.

I decided to scrap the part and start over. I rechecked the snugness of the rod journal spacers, and even though they felt correct, I can't help but think they were at least part of the problem. Since I'm now reasonably confident with the stability of the material, on my next attempt I'll likely finish the main journals before even roughing in the rod journals. - Terry

 

[thefishhunter]

Beautiful work as always. Round two should come out perfect.

I do have a question about your last post. What is the reason for the reduction In the compression ratio from the plans?

 

[mayhugh1]

Beautiful work as always. Round two should come out perfect.

I do have a question about your last post. What is the reason for the reduction In the compression ratio from the plans?

Thanks,
Reducing the compression ratio will reduce the combustion pressures and take some of the stress off the head gasket. This engine has some history with head gasket issues, and since I'm not building one to run on a dynamometer I thought I'd take some easy steps to make life a little easier later.

 

[dsage]

Hi Terry:
What's your reasoning behind roughing out the journals on the mill rather than avoiding all the back and forth and just taking it easy and turning them fully on the lathe? I can understand the time saving but it seems the careful re-measurement of TIR upon each return to the lathe would be time consuming also. No?
Just wondering. I never thought to do it that way.

 

[mayhugh1]

Dave,
The reason for roughing them out on the mill is that on the lathe I'd have to use the same deep grooving tool for roughing the narrow space between the webs. With just the .010" d.o.c. that I seem to be able make on steel with these tools on my lathe, it would not only take a long time but be pretty stressful. - Terry

 

[dsage]

Makes sense. and (as usual) a very smart idea. I'll give it try
Thanks

 

[wthomas]

Hi Terry:
Excellent work. From my experience on full scale cranks I would recommend you leave .005" to .010" on all the main and pin
diameters till after you have finished the sides of the pins and mains. Also I would indicate the side movement of the cheek
closes to the tailstock when you you tighten the tailstock. You could put enough pressure on the tailstock to make it move only
.001" then back the tailstock off and bring it back up to almost the same place with no bending pressure on the crank.
Another thing to consider is to rough mill the pins and sides close to round or round in the mill where you have less pressure on the rest
of the crank and then do the same for the mains. The less stock you have to remove between centers the less stress you are putting on the
pin and mains. This is the way I have found to have the least problems because you have less unbalanced weight stressing the centers.
Keep up the good work I really enjoy the photos and information.

 

[mayhugh1]

Hi Terry:
Excellent work. From my experience on full scale cranks I would recommend you leave .005" to .010" on all the main and pin
diameters till after you have finished the sides of the pins and mains. Also I would indicate the side movement of the cheek
closes to the tailstock when you you tighten the tailstock. You could put enough pressure on the tailstock to make it move only
.001" then back the tailstock off and bring it back up to almost the same place with no bending pressure on the crank.
Another thing to consider is to rough mill the pins and sides close to round or round in the mill where you have less pressure on the rest
of the crank and then do the same for the mains. The less stock you have to remove between centers the less stress you are putting on the
pin and mains. This is the way I have found to have the least problems because you have less unbalanced weight stressing the centers.
Keep up the good work I really enjoy the photos and information.

All great suggestions. Thanks a lot. I'm incorporating them in a new work flow while waiting on more material to arrive. I wish I'd planned for two, but I hate paying those shipping costs. - Terry

 

[propclock]

Just my opinion, My friend Dwight Giles reminds me when he makes his V8 cranks
they are rubber, and can be bent back into shape. A soft hammer can fix a lot of
the stress induced warping. Also he tends to over correct and wait a day, yep it grows back.
So in short, wack it ,or press it, don't cut it. Also another member of our club says,
This is why I built my tool post grinder. He grinds all of his cranks.
I truly appreciate all of you work and the sharing of your experiences.
Thank You.

 

[petertha]

This is why I built my tool post grinder. He grinds all of his cranks.

Propclock, not to detract from the thread, but I would really like to see how you arranged your TPG in a lathe environment with supporting tailstock. I have a Themac TPG that I use occasionally. It works well enough for cantilevered work extending from the jaw. I used it to grind cylinder liners that way for my 5-cyl radial. But as soon as I bring the tail stock into the equation, it wants to occupy the same real estate as the TPG even with the TS quill fully extended. I would probably have to run a 6" wheel to get TPG spindle to clear the (adjacent) TS. And then I'm running out of cross slide travel as it extends towards operator.

I've even set the TPG on the back side of work, mounted to a baseplate on my cross slide. That has some advantages. It eliminates some of the vertical stack-up associated with TPG on compound (less vibration from multiple sliding surfaces). Allows bigger wheels in theory, although I think my TPG is kind of orientated to max 3-4" based on pulley selection & fixed motor rpm. But doesn't solve the lateral conflict issue of TPG spindle & tailstock. Maybe a function on my lathe's apron casting footprint or tail stock size... but its generically a common 14x40 lathe.

I'll stop here & gladly start a new post on this subject because on the surface it seems like grinding is a great way to sneak up on a critical dimension like journal surfaces. I can post some pics that better show what I'm trying to describe with words.

 

[mayhugh1]

Propclock,
Thanks for the comments. In this particular case though, the TIR's result from the journals being oval and so bending the crankshaft won't help. The oval'ness's came from system flex during turning and was probably mostly caused by inadequate support between the rod journal cheeks while the main journals were being finished.

Petertha,
I feel your pain. I recently purchased a Themac J45 tool post grinder through ebay and ran into exactly the same problem. Mine required wheels with 1/2" center holes, but I couldn't find grinding wheels for it that would fit between the cheeks of my 3/8" wide journals. I then found a spindle adapter for 1/4" center hole wheels, but then the only wheels I could find with enough diameter to clear the adapter were Cratex-type resin bonded wheels. I wasn't sure these were suitable for what I wanted to do but I decided to give it a try anyway. I ran into the same interference with the tailstock. There was just no way to use it with a tailstock.

I also have an old Dumore TPG that I acquired through a local estate sale 15 years ago, It's 1/3 hp and doesn't have enough power for anything much larger than the mounted stones you would normally use in Dremel. It has even greater problems with the tailstock. I probably now have some $1k invested in tool post grinders, parts, and wheels for them and still haven't been able to do anything real with them. - Terry

 

[ICEpeter]

Propclock,
Thanks for the comments. In this particular case though, the TIR's result from the journals being oval and so bending the crankshaft won't help. The oval'ness's came from system flex during turning and was probably mostly caused by inadequate support between the rod journal cheeks while the main journals were being finished.

Petertha,
I feel your pain. I recently purchased a Themac J45 tool post grinder through ebay and ran into exactly the same problem. Mine required wheels with 1/2" center holes, but I couldn't find grinding wheels for it that would fit between the cheeks of my 3/8" wide journals. I then found a spindle adapter for 1/4" center hole wheels, but then the only wheels I could find with enough diameter to clear the adapter were Cratex-type resin bonded wheels. I wasn't sure these were suitable for what I wanted to do but I decided to give it a try anyway. I ran into the same interference with the tailstock. There was just no way to use it with a tailstock.

I also have an old Dumore TPG that I acquired through a local estate sale 15 years ago, It's 1/3 hp and doesn't have enough power for anything much larger than the mounted stones you would normally use in Dremel. It has even greater problems with the tailstock. I probably now have some $1k invested in tool post grinders, parts, and wheels for them and still haven't been able to do anything real with them. - Terry

Hello,
When I decided to grind the crankshaft for the two engines I was building, I run into the same problem regarding the reach of the grinding wheel into the journals with conventional aluminum oxide grinding wheels.
Consequently, I decided to use two dia.six inch CBN wheels with different particle concentration to rough out and final grind the journals for diameter and side clearance. The resulting tolerances and clearances came out very well. The unfortunate result was that my bank account took a serious hit, although I kind a expected that.
I posted quite a while ago some pictures on HMEM that showed the set up with the CBN wheels and my cam / crank grinder.

Peter J.

 

[petertha]

I seem to recall your post ICEpeter. If you could locate your link or find your pics I would certainly appreciate seeing them.

I created a new post on toolpost grinding. I'll leave it to you guys if you want to carry on discussion there or not. I'm starting to share Terry's sentiment. I had much bigger plans for the TPG compared to what I've been actually able to accomplish thus far. But that could also be lack of experience or good ideas on my part.
https://www.homemodelenginemachinist.com/threads/toolpost-or-other-grinding-in-the-lathe.32543/

 

[Foketry]

Propclock,
Thanks for the comments. In this particular case though, the TIR's result from the journals being oval and so bending the crankshaft won't help. The oval'ness's came from system flex during turning and was probably mostly caused by inadequate support between the rod journal cheeks while the main journals were being finished.

Petertha,
I feel your pain. I recently purchased a Themac J45 tool post grinder through ebay and ran into exactly the same problem. Mine required wheels with 1/2" center holes, but I couldn't find grinding wheels for it that would fit between the cheeks of my 3/8" wide journals. I then found a spindle adapter for 1/4" center hole wheels, but then the only wheels I could find with enough diameter to clear the adapter were Cratex-type resin bonded wheels. I wasn't sure these were suitable for what I wanted to do but I decided to give it a try anyway. I ran into the same interference with the tailstock. There was just no way to use it with a tailstock.

I also have an old Dumore TPG that I acquired through a local estate sale 15 years ago, It's 1/3 hp and doesn't have enough power for anything much larger than the mounted stones you would normally use in Dremel. It has even greater problems with the tailstock. I probably now have some $1k invested in tool post grinders, parts, and wheels for them and still haven't been able to do anything real with them. - Terry

I had the same tailstock interference problem, i solved it through these diamond grinding wheels.
Their are available with diameters from 80 to 150 mm and thicknesses from 10 to 20 mm, the body is aluminum and the internal hole can be reduced or enlarged.
Their removal capacity is higher than normal grinding wheels.

 

[wthomas]

Hi Terry:
I forgot to tell you if you mount the end of the crank in a four jaw chuck and work between it and a steady rest in the middle of the crank
you will have a much stronger setup to machine the mains. You may not be able to do this with the steady rest on the middle main for lack
of space but if you go to the next main and run it in a steady rest with a piece of heavy leather belting as well as the tailstock you should
have lots of support. If you use an offset hole in a support sleeve on another crank pin in the steady rest you can machine the pins this way.
The closer to the supported (chucked end) of the crank the stronger the setup and less flexing. Just think how much stronger your straight
pins are compared to the offset split pins that Buick run on the even fired V6. The crank blank was 7" in diameter and 24"s long. When they
turned the ends and added throw blocks they had a WHOLE LOT of unbalanced weight swinging in the lathe between centers. It would
have been better to do like you are and to mill most of the unbalanced weight off.
Also if you are unable to grind the pins and mains consider using a narrow flat belt sander st finish them.
Keep looking and you will find a solution!
Bill Thomas

 

[johwen]

Hi Guys,
Faced with machining a crank for a 4cylinder Sealion engine I decides to build my own crankshaft grinder from the plans published in Strictly I C mag. I machined up the crankshaft in the normal way after Centre drilling the ends of the material to accommodate the centres of the mains and crank pins. I turned all journals leaving the .005 oversize. Mounting the shaft in the grinder then it was easy to grind mains all in line and the crankpins all to size. The grinder was relatively easy to make and it's sitting there waiting for the next crank. Making the grinder was a good exercise in engineering practice. Cheers. John

 

[G54AUST]

Hi Guys,
Faced with machining a crank for a 4cylinder Sealion engine I decides to build my own crankshaft grinder from the plans published in Strictly I C mag. I machined up the crankshaft in the normal way after Centre drilling the ends of the material to accommodate the centres of the mains and crank pins. I turned all journals leaving the .005 oversize. Mounting the shaft in the grinder then it was easy to grind mains all in line and the crankpins all to size. The grinder was relatively easy to make and it's sitting there waiting for the next crank. Making the grinder was a good exercise in engineering practice. Cheers. John

'Afternoon John.

The SIC plans are from issues 63, 64 and 65 ???


Regards,

Trevor,
Melbourne, AU

 

[ICEpeter]

I seem to recall your post ICEpeter. If you could locate your link or find your pics I would certainly appreciate seeing them.

I created a new post on toolpost grinding. I'll leave it to you guys if you want to carry on discussion there or not. I'm starting to share Terry's sentiment. I had much bigger plans for the TPG compared to what I've been actually able to accomplish thus far. But that could also be lack of experience or good ideas on my part.
https://www.homemodelenginemachinist.com/threads/toolpost-or-other-grinding-in-the-lathe.32543/

I seem to recall your post ICEpeter. If you could locate your link or find your pics I would certainly appreciate seeing them.

I created a new post on toolpost grinding. I'll leave it to you guys if you want to carry on discussion there or not. I'm starting to share Terry's sentiment. I had much bigger plans for the TPG compared to what I've been actually able to accomplish thus far. But that could also be lack of experience or good ideas on my part.
https://www.homemodelenginemachinist.com/threads/toolpost-or-other-grinding-in-the-lathe.32543/

Hello Petertha,
I sold the cam / crank grinder a while ago and the link to it is SOLD - For sale Camshaft - Crankshaft grinder / accessories
When using the grinder, I had the CBN wheels custom made with a specific width and with corner radius for the crank journals. I picked CBN for the wheels because, supposedly, diamond wheels don't like the carbon in steel and CBN wheels permit dry grinding without coolant.
To see other info about the grinder and other stuff, you could take a look at my list of posts. They give you quite an overview of posts I contributed at HMEM.

Peter J.

 

[petertha]

Hello Petertha, I sold the cam / crank grinder a while ago and the link to it is SOLD - For sale Camshaft - Crankshaft grinder / accessories
Peter J.

Ah yes, that's the grinder I recall. Work of art!
What kind motor did you use? (it has the look of a Sherline?).

 

[ICEpeter]

Ah yes, that's the grinder I recall. Work of art!
What kind motor did you use? (it has the look of a Sherline?).

Petertha,
You have good eyes. Yes, it is a Sherline variable speed motor system (as used for their lathe drives) and a Sherline industrial spindle that I used when building the tool post grinder for use in the cam / crank grinder.