CNC Machinist: If Machining a 2 Stroke Crank?

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Armilite

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pictsidhe

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That's what Phasing the Crank is pictsidhe, your Aligning the Crank Wheels, which also Aligns the PTO and Mag Shafts that the Bearings go on, so your Runout is .001" or less on the Shafts. Reading should be taken off the Shafts, but some People do it off the Bearings. They usually use a Lead Hammer 5+lb. Today they have some nice Fixtures that Help to Align them faster, but cost a $1000+.
Maybe 'phasing' is an example of incorrect English usage in the USA. It's pretty common...

I do know how to zero the runout on a crank, but I'm really slow compared to a wrinkly old guy who does it for a living. I've never seen or heard of anyone using a lead hammer to do it. You have to smack the cranks pretty hard sometimes and lead is awful soft to last very long. You do need something softer than your crank, or you'll dent it.
 

Armilite

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Maybe 'phasing' is an example of incorrect English usage in the USA. It's pretty common...

I do know how to zero the runout on a crank, but I'm really slow compared to a wrinkly old guy who does it for a living. I've never seen or heard of anyone using a lead hammer to do it. You have to smack the cranks pretty hard sometimes and lead is awful soft to last very long. You do need something softer than your crank, or you'll dent it.
=======================================

Phasing, is talking about Aligning the Crank Wheels, Runout is talking about a Measurement of the PTO/MAG Shafts. Some People have a Secure Stand with a Box with just a Square Chunk 6' x 6" x 3" of Lead, and grab Crank by both ends and Slam Crank Wheel against the Lead Block. Easier to Cast 6" x 6" x 3" Lead blocks.

A nice Crank Rebuild Video showing some Pro Tools. One exception, Never Use a Press or Bearing Tool on the MAG end without the Nut on.
https://www.youtube.com/watch?v=_1T_1SzD2Og

2-Stroke Crank Rebuild and True. Showing one the New Jigs out. Expensive, but 4-5 Crank rebuilds can Pay for it.
https://www.youtube.com/watch?v=9h-AbRQLGgA

Fastest crankshaft rebuild, balancing. Makes me laugh every time I watch it. Be interesting to see How True they are when he's done.
https://www.youtube.com/watch?v=r8lCGTltAm4
 

pictsidhe

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I'm not confused because i don't know how to measure or true a crank, I'm confused because you are using incorrect terminology.

If you're going to insist on 'phasing' cranks, at least use proper units. It's usually an angular measurement, though time is sometimes used.
 

proppastie

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I think we understand what he means,...its a shame the manufacturer did not have timing marks to line up, it would make things so much easier.
 

Armilite

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Good Article on "RD400 Crank Rebuild Guide." I suggest you Copy and Paste this whole Article into MS WORD and Save as a PDF.
http://www.rrracing.co.nz/crank/

When the Crank Wheels are Out of Alignment, it is also called Out of Phase by Crank Rebuilders. Once the Crank Wheels are in Phase or Alignment if that makes it easier for you to understand, then the Runout of the (2) Shafts between Centers is Checked. The Crank Wheels and PTO/MAG Shafts are usually 99% One Piece. Those Shafts can also be Bent also. So when Crank is apart, mount each PTO & MAG Half between Centers and check Runout of the Shaft vs the Crankwheel. There is a lot of Poor Machining Tolerances in the World.

The photo on the Left would be considered Severely Out of Phase or Alignment.
 

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Armilite

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phase noun
\ ˈfāz \
Definition of phase (Entry 1 of 2)
1: a particular appearance or state in a regularly recurring cycle of changes phases of the moon

2a: a distinguishable part in a course, development, or cycle the early phases of her career

b: an aspect or part (as of a problem) under consideration

3: the point or stage in a period of uniform circular motion, harmonic motion, or the periodic changes of any magnitude varying according to a simple harmonic law to which the rotation, oscillation, or variation has advanced from its standard position or assumed instant of starting

4: a homogeneous, physically distinct, and mechanically separable portion of matter present in a nonhomogeneous physicochemical system

5: an individual or subgroup distinguishably different in appearance or behavior from the norm of the group to which it belongs
also: the distinguishing peculiarity in phase

: in a synchronized or correlated manner
 

Larrywal

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If you wanted to Machine a 2 Stroke Crank which is Pressed together in a Hyd Press, let's just use a Rotax 277UL Crank to make it Simple. You can Buy Rod kits with Crank Pins and Bearings fairly cheap. You can Buy the Crank Bearings. You can even still Buy some Replacement PTO Ends for, the 377/447, 503, 521/582, and 670. I haven't ever found anyone who makes the Mag Ends.

Most Crank Wheels Avg around 4.0 to 5.0" OD Max and the PTO/MAG Ends each Avg around Max 6.0" Long, so a piece of raw stock 5.0" x 6.0" with a little extra length for Clamping in a Lathe.

My question is, with a piece of raw Stock that has already been Faced off on both ends and Center Drilled, and OD turned for the Max Crank Wheel OD Spec, could a CNC lathe with a Tool Changer, finish the Crank in one setup?

1. Finish PTO OD Contour
2. Finish PTO Center Drill Hole to Size & Tap the End
3. On doing the Mag End Contour and Thread the End OD for Flywheel Nut.
4. The Bore & Ream Crank Pin Hole for whatever Stroke you're using?

A CNC Lathe something like this one, a 1994 Okuma-Howa ACT-20 with FANUC 18-T control Includes 8" chuck.
In my experience the answer would be no. Even if you were able to machine it to the best of the Lathes ability you would still have to heat treat and after heat treating do a finish grind on the Id of the crank pin bore. There is a factory that has had some success in cutting out a lot of the manufacturing and metrology steps that were once necessary for a quality product. It is called China. Lol. But seriously if you want to make a prototype you should be able to do it on your manual lathe. Figure out what carbon or alloy steel blank you want to start with by doing some research on what other people are using in similar applications. Machine it to the best of your ability, then heat treat based on the alloy you used then finish grind with a toolpost grinder or have a shop do any of the steps that you are not comfortable doing. Put it together and run it on a ground unit or hovercraft to check your work. If it works out then have a shop give you a quote on making 10 more.
 

proppastie

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then heat treat based on the alloy you used
If you wanted a different design. ...clean sheet. ...might have full beatings pressed onto the crank and into the rod.
That would eliminate the need for heat-treat and grind.
Not sure how it would work overall considering the extra rotating mass though.
It would be something different.
 
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Armilite

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In my experience the answer would be no. Even if you were able to machine it to the best of the Lathes ability you would still have to heat treat and after heat treating do a finish grind on the Id of the crank pin bore. There is a factory that has had some success in cutting out a lot of the manufacturing and metrology steps that were once necessary for a quality product. It is called China. Lol. But seriously if you want to make a prototype you should be able to do it on your manual lathe. Figure out what carbon or alloy steel blank you want to start with by doing some research on what other people are using in similar applications. Machine it to the best of your ability, then heat treat based on the alloy you used then finish grind with a toolpost grinder or have a shop do any of the steps that you are not comfortable doing. Put it together and run it on a ground unit or hovercraft to check your work. If it works out then have a shop give you a quote on making 10 more.
=====================================

I think I didn't make myself clear enough. If you're making the PTO/MAG Ends then Yes you have to do all that stuff. But, if you're using most of the Parts that have been already machined and hardened. Like the 277UL was (72mm x 66mm) 268.8cc so it has a 66mm Stroke with a PTO that is Tapered 30mm 1:10. The only other Rotax Single that used a similar PTO but a different Stroke was the 250 Type 253 that used (72mm x 61mm). Both used 120mm Rods. Which you have the option to use a 550F (76mm x 61mm) 553.6cc Twin Cylinder to make a (76mm x 61mm) 276.8cc.

But you also have options to dismantle some Twin Cranks for there PTO/MAG ends, to make other Strokes, 61mm, 64mm, 66mm, 68mm, 70mm, are the most commonly used. Most of the Cranks all used a 24mm Crank Pin, and some used different Lenght Rods, 120mm, 125mm, 132mm. Like the 277 used a 66mm Stroke and if you used longer Rods, you need a thicker Base Plate/Gasket to make things line up. Some used different Size Crank Bearings. The 70mm Stroke 670 Crank also used a bigger PTO 33mm 1:7.5 which needs adjustments for depending on what reduction drive you use. On the Crank Wheels you may need to turn the OD Smaller and you may need to turn the Outside down to fit the Case. The Rod & Crank Pin used, dictates the Width, Side to Side. Like a 277 uses a 24mm x 57mm Crank Pin and the 670 uses a 24mm x 53mm Crank Pin. So you would need to Shim it. For most people who what more hp at same Stock rpm, it's easier to just use a Tuned Pipe, maybe raise the CR, or Big Bore it. Max Bore a 277, 503, 550, is 82mm. So an (82mm x 70mm) 369.8cc
 

MadRocketScientist

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A pressed crank does require a full beating to get it straight and true.......

...and the beatings will continue until morale improves.....
From what I have been reading about pressed motorcycle cranks, if one uses an accurate custom jig when pressing the crank, no adjustment should be needed. hold the cranks parts in perfect alignment as it is being pressed together apparently.
 

Armilite

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From what I have been reading about pressed motorcycle cranks, if one uses an accurate custom jig when pressing the crank, no adjustment should be needed. hold the cranks parts in perfect alignment as it is being pressed together apparently.
=============================

True, a Crank Jig (Expensive $1000) unless you can make your own, can get it real close, but not Perfect! Factory Tolerances can be .003" to .004", Racers Phase them to .001" or better and then either Pin, Weld, or Epoxy Glue today.
Crankshaft Jig
 

proppastie

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If I were designing a pressed crank to be built at home I would have press fit dowel pins for exact alignment,....to be removed after the assembly is pressed together. It would have full bearings on soft shafts and needle bearing rollers on hardened shafting for the rod...... This is extra operations in the production environment so it is not done that way. They do not even have alignment marks because those are extra operations. Every extra operation costs more money.

. But, if you're using most of the Parts that have been already machined and hardened.
that works too. if you have the parts or can get them.
 
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