Inline 4, Two Stroke

[PRiggs78]

Made a little more progress earlier today. Unable to finish head assembly due to USPS mail woes. Seemingly the material is lost or stolen at Wisconsin facility (yeah, mail-in voting will be great!).

Anyhow, did some crank work today with 1144 steel. Journal size is 5/16" undersized, paired to a reamer.

Made a jig to place in the lathe to get the essentric rotation going, but do not trust it! May have to break down and get a four jaw chuck to finish the task.

The idea was to use jig on chuck end, on the tail stock side (larger crank diameter side) drill some holes 90 degrees apart so live center can support crank and give me point to rotate the crank 90 degrees so the various connecting rod journals can be cut. Have to think a little bit more on this....

 

[PRiggs78]

Made a little more progress earlier today. Unable to finish head assembly due to USPS mail woes. Seemingly the material is lost or stolen at Wisconsin facility (yeah, mail-in voting will be great!).

Anyhow, did some crank work today with 1144 steel. Journal size is 5/16" undersized, paired to a reamer.

Made a jig to place in the lathe to get the essentric rotation going, but do not trust it! May have to break down and get a four jaw chuck to finish the task.

The idea was to use jig on chuck end, on the tail stock side (larger crank diameter side) drill some holes 90 degrees apart so live center can support crank and give me point to rotate the crank 90 degrees so the various connecting rod journals can be cut. Have to think a little bit more on this....

Went back to it.... Came up with a solution, I think. Seems rock solid.

Round stock with offset hole for crank main to ride in at the appropriate distance. Milled three equal flats at 120 degrees so the little chuck can bite safely. Drilled and tapped some holes and slot cut 90 degrees from drilled and tapped holes. Cinches down on the crank tightly.

Tomorrow the attempt to finish it up!

 

[PRiggs78]

Didn't go so well today. Bummer. Truly annoyed and upset.

Think my Grizzly G0765 14" lathe just doesn't have the rigidity to accomplish the task alone. Tried the work around to obtain necessary rotation, holding, etc... Started at the tail side and planned working toward the chuck. Got nearly finished and the damn thing hitched a ride on top of the cutter resulting in a mangled mess.

Anyone have some tips not found on YouTube I've already seen? Or, someone with greater skill set and tools want to turn me one?! I'll pay, of course. Simple crank design, I thought. Guess not.

Back to the drawing board....

 

[Sprocket]

If you were going to use a live center in the tailstock, can you drill the same center holes in the other end and turn your part between centers?
I've done this with single cylinder crankshafts, and if you can get the holes aligned (both ends the same) I think it should work. Better yet,
see gbritnell's write up here.
Holt engine-crankshaft machining-step by step - The Home Shop Machinist & Machinist's Workshop Magazine's BBS
Good luck
Doug

 

[PRiggs78]

I did think about the method of drilling five holes on each end of the round stock and use a dog and dead center on chuck side and live on tail stock; may give it a go, actually.

Honestly, I think my issue became the lack of rigidity in my machine once the crank spins an unbalanced mass. Typically pretty rigid, but this project made the lack known.

Purchased a nice parting tool.... Too bad it is too large for my machine. Was really hoping to use it.

Such a slow process standing there turning a thou or two at low rpm.

I may get spunky and use [try] the rotary table and mill the connecting rod journals, turn the rest down on the lathe.

 

[SmithDoor]

Your lathe will work.
Just use 7° to 10° rake on your tool bit.
I would use a mill to ruff out.
There other trick you do but have all ready did some machining.

Dave

Didn't go so well today. Bummer. Truly annoyed and upset.

Think my Grizzly G0765 14" lathe just doesn't have the rigidity to accomplish the task alone. Tried the work around to obtain necessary rotation, holding, etc... Started at the tail side and planned working toward the chuck. Got nearly finished and the damn thing hitched a ride on top of the cutter resulting in a mangled mess.

Anyone have some tips not found on YouTube I've already seen? Or, someone with greater skill set and tools want to turn me one?! I'll pay, of course. Simple crank design, I thought. Guess not.

Back to the drawing board....

 

[777engman]

If you want send me the drawing for your crankshaft and I'll make it for you.
Dean

 

[Jamie Barton]

I had similar problems making a crank for the tiny inline 4, four-stroke a few months ago. In the end I roughed out on the mill then made a very small tool post grinder to round off and finish. It worked well but I must've put a good 2 days solid work into it, maybe more. My tiny grinder didn't have much guts to it but because of that it excerts very little force on the work. Also very messy, makes metal shards as light as dust.

 

[Jamie Barton]

My ridiculously small tool post grinder does use elastic bands as drive belts.. But it worked

 

[davidyat]

Go to this HMEM link:

https://www.homemodelenginemachinis...ne-build-2x-scale-up.25083/page-5#post-302221
This should be page 5 and scroll down for information on how Bazmak did his crank. After I botched up 2 cranks, I learned to make biscuits that I would fit snugly in between the journal webs. Then I could put some pressure on the assembly with the tail stock live center to hold everything rigid. On my third try, it worked.
Grasshopper

 

[PRiggs78]

Go to this HMEM link:

https://www.homemodelenginemachinis...ne-build-2x-scale-up.25083/page-5#post-302221
This should be page 5 and scroll down for information on how Bazmak did his crank. After I botched up 2 cranks, I learned to make biscuits that I would fit snugly in between the journal webs. Then I could put some pressure on the assembly with the tail stock live center to hold everything rigid. On my third try, it worked.
Grasshopper

Yes sir. The biscuit method was totally overlooked. Definitely putting that in the learned folder.

 

[PRiggs78]

If you want send me the drawing for your crankshaft and I'll make it for you.
Dean

Tried the little mail icon up top and generated a "conversation"... Not sure that is the mail feature here...

 

[Tim Wescott]

For the balance problem, you could always counterweight your assembly. I don't know how bad the Grizzly is, but a crankshaft is kind of the essence of long and flexible -- it may not be the lathe that's the problem, particularly if it's cantilevered out from a chuck instead of being held between centers.

 

[PRiggs78]

That's somewhat inherent to making a crankshaft, isn't it? The whole mess is unbalanced when cutting the con journals. I mean, the one journal being cut is on axis to the bore. The exception are all the rest. Unless one is cutting main journals, which is centerline of entire part.

Am I missing something here? Now, CNC setup can do it the other way keeping shaft centered on main journal axis with the head going up and down.

 

[SmithDoor]

Once you did one or two it will be easy. CNC is ok but setup is high for tooling you would need.
Remember you have to program the CNC lathe or mill.

Dave

That's somewhat inherent to making a crankshaft, isn't it? The whole mess is unbalanced when cutting the con journals. I mean, the one journal being cut is on axis to the bore. The exception are all the rest. Unless one is cutting main journals, which is centerline of entire part.

Am I missing something here? Now, CNC setup can do it the other way keeping shaft centered on main journal axis with the head going up and down.

 

[PRiggs78]

A wee bit of progress made. Very proud of how this head turned out being the first engine ever for me. Didn't go too overboard with cooling fins since this engine will have a fan on front like a conventional 4 cylinder car engine. Plans to make a water cooled head if this ends up in a boat...

Been researching blower designs and the necessary arithmetic to calculate volume, etc. Learned a bit so far, which has been rather enlightening.

 

[Steamchick]

I hope you have designed the Crank correctly. In "industry", cranks are not designed for minimum material so much as for stiffness. Although car engine cranks are VERY flexible. The rule is that too much crank flex, although OK for "simple stress", will fatigue, if it doesn't wear out the bearings first! Now I don't know what loads you have envisaged for the piston loading + inertial loading, but the central main bearings look slender to me? That says not a lot compared to the Big-end journals at around 2/3rds the diameter. I wonder why the outer shafts are "so large" in comparison? - I'll be very interested top hear how you designed this one? (No criticism intended, just this is so far removed from my experience I don't understand it, and would like to?). I do appreciate that engines for models (as opposed to "models of engines") are so small in comparison to "Human-sized" engines, that many rules are the same but the results look quite different. (as Linear, square, cubic and quartic rules all apply to size, area, stiffness and stress).
Incidentally, I mad a twin big-end (180deg) crank some years ago on a very weak (80 year old) 3" lathe: by mounting a small 3 law chuck off-set in a 4 jaw chuck, and by holding the main end of the crank in the 3 jaw chuck.... VERY careful machining did it in 2 steps, one per journal. (from a Stuart iron casting). Of course the mains were pre-machined with ends centred. The tool used was a parting tool with a thou recess in the middle, and radii on the corners. a just under half the width of the journal, I traversed sideways back and fro while adding a thou or 2 per traverse, until sized. Then lapped using mole grips and emery. to polish the last thou.
But journals were huge compared to yours: 1/4" dia.
Hope that helps?
Thanks,
Ken

 

[Steamchick]

Frankly, I would have made your from "stock" sizes in reamed plates, and silver soldered the whole in a jig, rather than machined from solid?
K

 

[PRiggs78]

I hope you have designed the Crank correctly. In "industry", cranks are not designed for minimum material so much as for stiffness. Although car engine cranks are VERY flexible. The rule is that too much crank flex, although OK for "simple stress", will fatigue, if it doesn't wear out the bearings first! Now I don't know what loads you have envisaged for the piston loading + inertial loading, but the central main bearings look slender to me? That says not a lot compared to the Big-end journals at around 2/3rds the diameter. I wonder why the outer shafts are "so large" in comparison? - I'll be very interested top hear how you designed this one? (No criticism intended, just this is so far removed from my experience I don't understand it, and would like to?). I do appreciate that engines for models (as opposed to "models of engines") are so small in comparison to "Human-sized" engines, that many rules are the same but the results look quite different. (as Linear, square, cubic and quartic rules all apply to size, area, stiffness and stress).
Incidentally, I mad a twin big-end (180deg) crank some years ago on a very weak (80 year old) 3" lathe: by mounting a small 3 law chuck off-set in a 4 jaw chuck, and by holding the main end of the crank in the 3 jaw chuck.... VERY careful machining did it in 2 steps, one per journal. (from a Stuart iron casting). Of course the mains were pre-machined with ends centred. The tool used was a parting tool with a thou recess in the middle, and radii on the corners. a just under half the width of the journal, I traversed sideways back and fro while adding a thou or 2 per traverse, until sized. Then lapped using mole grips and emery. to polish the last thou.
But journals were huge compared to yours: 1/4" dia.
Hope that helps?
Thanks,
Ken

The inner main journal size is 5/16" with ends at 3/8", modeling off of a glow engine size. Inner main bearings will be brass, ball bearings supporting crank ends.

Not certain how this will pan out! It's an experiment for sure!

 

[Steamchick]

That sounds pretty good, what size big-end journals?
K