Looking for advice on making machine shafts.

[hennebury]

I am new to metalwork, so I will ask for your indulgence.
I rebuild old woodworking machinery, make a few parts etc.
I have a DSG lathe and a surface grinder
I need to make half a dozen small machine shafts for some old machines that I am rebuilding.
The shafts are usually pretty beat up when I get them, so I am going to have a shot at making new ones.
The Original shafts are DIN 1.6582 (34CrNiMo6)
I plan on using this 4340 for the new ones.
They have three bearing journals on the axis and an double bearing journal offset.
My thoughts were to turn the shaft down to 24mm finished size, make a collet with the offset bore to hold the dressed rod, use that collet in the Jacobs chuck, machine the offset, then finish in the Jacobs chuck with a standard collet.

This is the material that I was considering.

4340 HR HT BAR 285/363 BHN ASTM A434 CL BD
1-1/4 RD S/C 1'3.5" (15.5")




Any advice on the material or machining would be appreciated.

 

[RJT]

In order to get the journals to run true to each other (be concentric) , the right way to do it is put centers in each end and do them all at the same time turning (or grinding) between centers. Your method will not be nearly as accurate. I would imagine these diameters need to run concentric. This is not a beginners job.

 

[hennebury]

In order to get the journals to run true to each other (be concentric) , the right way to do it is put centers in each end and do them all at the same time turning (or grinding) between centers. Your method will not be nearly as accurate. I would imagine these diameters need to run concentric. This is not a beginners job.

Maybe i didn't explain it correctly. The three journals that are on the center axis will be turned as you say.
The offset journal will be turned in the custom made collet with the offset bore.

 

[michiganbuck]

RJT nailed it...
It is darn near impossible to make a decent bearing machine shaft with not taking the finish cuts from between centers. The best collets can run out .0002 so in the turn around you can easily have .0004 or a half thousandth error.

Out of a good 4 jaw the point of indicating might be zero and down the wobble the part is likely to run out a few thousandths.

Anything other than between centers is a hack job.

bearings going wobble, wobble can make a lot of vibration along with wearing out the bearings.

If the part can not have centers, then you make it between centers and then part off the centers.

 

[RJT]

I didn't see the offset journal, now I understand the question. Yes, bore an emergency collet off center to turn the offset journal. It's going to be really unbalanced, so you may need counter weights somehow attached to the shaft or really slow RPM. Another option is two sets of centers on each end, but they have to be put in oriented to each other. Or use a 4 jaw for the offset.

 

[michiganbuck]

Still, the three bearing diameters should be run between center IMHO

 

[RJT]

Yes, bearing journals between centers.

 

[hennebury]

I didn't see the offset journal, now I understand the question. Yes, bore an emergency collet off center to turn the offset journal. It's going to be really unbalanced, so you may need counter weights somehow attached to the shaft or really slow RPM. Another option is two sets of centers on each end, but they have to be put in oriented to each other. Or use a 4 jaw for the offset.

I think that if I machine the three center axis journals between centers and the main shaft to finish size first, then place the shaft in the offset collect, trim the end off, redrill it with a new center hole, and machine the offset in the custom offset collet and a center on the outboard end, then trim the end again to finish length. The offset is very small, but I will take it easy on the speed, I will see if I need counterbalance weights.

Thanks.

 

[ratbldr427]

Adding the new center is how I have done it, shouldn't need any counterbalance as there is no need for optimum speed.

 

[stephen thomas]

Journals between centers as has been covered.

If the part with fit in the bore of your lathe, the quickest way to do the offset is in a good 4 jaw.
indicate radially to establish offset amount. Indicate axially to be sure the 4j grips in line.

If necessary you can still drill a new center hole and use the TS.
Or shrink on a stub to drill into.
Just be certain the part is parallel in the 4j to the lathe CL when drilling or turning.

What kind of machine?
MAKA mortiser? or?

smt

 

[hennebury]

Journals between centers as has been covered.

If the part with fit in the bore of your lathe, the quickest way to do the offset is in a good 4 jaw.
indicate radially to establish offset amount. Indicate axially to be sure the 4j grips in line.

If necessary you can still drill a new center hole and use the TS.
Or shrink on a stub to drill into.
Just be certain the part is parallel in the 4j to the lathe CL when drilling or turning.

What kind of machine?
MAKA mortiser? or?

smt

Thanks Stephen, Yes its for Maka mortisers, and yes it will fit the bore of the lathe. My reason for thinking about a collet with an offset bore to use in the Jacobs chuck, was for speed, accuracy and consistency, also for doing more at a latter date. I have a few machines to rebuild, and the shafts are in rough shape. I would rather make new ones. I repaired a few before, by thermal spray and re-machining, My thoughts were making new ones is probably a better solution, so just thinking about the best way to do it. Also I haven't used this material before, so I am wondering what it is like to machine. I will probably make six shafts at this time.

 

[Bill D]

Does it really matter if the offset distance is accurate or is there some wiggle room in that dimension? I see this like making a crankshaft. Some crank shafts are machined in short sections then glued together with tight fits and lock tite products.
Bill D

 

[hennebury]

Does it really matter if the offset distance is accurate or is there some wiggle room in that dimension? I see this like making a crankshaft. Some crank shafts are machined in short sections then glued together with tight fits and lock tite products.
Bill D

Hi Bill,
The only information I have is on the spec sheet from the 70's, but it shouldn't be too fussy on the offset as the crank is part of a system that provides an infinite variable ( within the parameters) throw on part that it moves. You can adjust the amount of throw the crank supplies, so it shouldn't be too critical, it won't interfere if its a thou or two one way or the other.

 

[thermite]

Hi Bill,
The only information I have is on the spec sheet from the 70's, but it shouldn't be too fussy on the offset as the crank is part of a system that provides an infinite variable ( within the parameters) throw on part that it moves. You can adjust the amount of throw the crank supplies, so it shouldn't be too critical, it won't interfere if its a thou or two one way or the other.

There are FAR easier - and more "general purpose" - means to avoid messing with generating an offset-bore in an emergency collet... and only getting the ONE size for your effort, each go, even so.

A) I keep an ER 40 "plate mount" through bore master collet. About $70.
Or one can pull the camlock studs out of a D1-(x) temporarily.

(I also have a spare "plain back" 5C key-operated unit that is NOT mounted to a backplate for use the same way)

- In any case, offset the entire plate in the 4J and the collet portion now covers the full range of ER 40 collet set (or 5C...) from just above zero to max diameter. It now also repeats near-as-dammit exactly to the same offset, one part after another.

B) Same again, ER 40 and 5C in both hex and square tooling "blocks"

All of these can be used ON center as well as set-over, not only on the lathe, but for bench, mill, Rotab, Dividing Head, or grinder fixturing too, and for all tasking any time, any size, going forward.

In either case, NO turning nor boring required at all, just grab and doo the 4J foo.

Which is why the chuck on my Ellis DH is a 4J, not the "usual" 3J, too.

Beside, proud to not even OWN a 3-J 'prentice chuck..



2CW

 

[hennebury]

I will certainly look into what you have suggested, thank you. So much to learn.