[M-man]

How do I correctly center and machine long shafts? About 100mm dia and 2000mm long. I do have hydrualic steady reast. The material are a bit bent and have a various quality of surface before the machining..

[ctate2000]

How do I correctly center and machine long shafts? About 100mm dia and 2000mm long. I do have hydrualic steady reast. The material are a bit bent and have a various quality of surface before the machining..

What type of machine are you using?

[M-man]

I am using a big lathe.

[g-codeguy]

I am using a big lathe.

Guess so! Part is almost as long as the lathes I run. LOL. Whenever I run a long (for my machine) shaft, I like to hold short, face and center drill all parts first. If the first diameter is short, I may even rough it in at this time. Do you have a way of supporting the rear if done this way? Homemade spindle guide, maybe?

[ctate2000]

Mark center with the trusty center finder in you adjustable square set. Center punch it. Drill it using portable drill motor and center drill. The care you take in locating the center will effect the amount of initial run out and the amount of stock you have to remove for clean up. So be careful. This is my preferred method.

You can also center it in the steady rest and then use the tail stock to drill it. Sometimes it is difficult to get enough RPM to allow the center drill to cut effciently.

[M-man]

If the stock arent straight the steady rest forces the 100mm bar into position, so if I clamp it with the steady rest and do my center, it will not be true to the chucked side of stock when unclamping it. Mabe I could make somekind of plate with adjusting screws and a center so that I can get som support from the tailstock and machine a true surface for the steady rest before machining the center ?

[Mazaholic]

Mark center with the trusty center finder in you adjustable square set. Center punch it. Drill it using portable drill motor and center drill. The care you take in locating the center will effect the amount of initial run out and the amount of stock you have to remove for clean up. So be careful. This is my preferred method.

Thats the best way M-man.
Then chuck the end of the bar and put the center on the other end.
Turn down a small section on the end with the center.
On the end where it is chucked,make a small turnback for the steady rest.
Now you can flip the bar and the chuck and steady rest will be aligned properly.
Then you can center drill that end,bring the center up,remove the steady rest and turn the entire bar without worry of run out,and the chuck will have a good hold on the material.

[Geof]

Make a ring, is small enough to fit inside your steady rest and large enough to fit over your 100mm dia., with setscrews that can be used to center the shaft inside the ring. You may need four pairs of setscrews so the ring is stable.

Use a four jaw chuck to hold one end of the shaft and the ring in the steady at the far end and you can adjust the chuck jaws and the setscrews in the ring so that you average out the bend and uneven OD of the shaft.

Drill a center at one end then turn it around and do the other.

[Delw]

How do I correctly center and machine long shafts? About 100mm dia and 2000mm long. I do have hydrualic steady reast. The material are a bit bent and have a various quality of surface before the machining..

it all depends as you left a few things out

does the shaft have any id work all ready done? Very important.
how much stock are you taking off the shaft? if its more(double) than the shaft is bent then your fine, if its less than the shaft is bent then you need to straighten the shaft ( now that I calculated the dia, I hope you have a very big press LOL)

Shaft work can be really simple or can be very complicated, we tend to make things more complicated than they really are.

A 4" shaft 78 inch long wont fit properly in the chuck Jaws leaving 2-3 inches haging out to cut it., if you have a through spindle you need too make a sleeve so the shaft doesnt get much run out in the back were its un supported. while you might think its ok, your center drill will run out big time cause of the movement in the back.

Geof hit it pretty good. with the collar for the steady rest. that trick works very well. for getting the shaft to run as true as possible.
however if you have lots of stock to take off. just put the steady rest on the front end (5-6 inches from the end) and indicate the front part, putting the back part in a 3 jaw, cut an od thats true and maybe oversized. then cut your jaws to hold the o.d.. put the newly cut O.D. in the jaws.
then put the steady rest on the front 3-4 inches of the part and center drill ( with a very big center drill) center drill and pop your center in there.

if your going to use a steady rest for cutting with out a center then just omitt the center drill part. You may have to run both a center and a steady rest on big shafts we had to do that as a center wouldnt support the part.

you can also hang it out half way using the geof method and use a center to steady it cut your bent section so your steady rest fits true.


we had a 30 foot machine between centers used to run shafts all the time.

[ctate2000]

Nothing you can do with a center to make a bent shaft straight. If bent beyond an acceptable limit you have no choice but to straighten it. Or buy bigger stock.

[DareBee]

To get stock resting in a steady rest centered properly on the tailstock, I use a rotating chuck in the tailstock. Install an indicator in the chuck and turn it around the part using the steady rest screws to get it centered. Once it is centered you can center drill it and (obviously) you can now hold that end with your center.

If you are just turning it while holding in the steady, use the method above for initial setup, and you can adjust the taper out of the part during the turning process by adjusting the part forward or backward as needed with the steady.

You can also use a large version of the afore mentioned rotating chuck to hold the part while turning.

[M-man]

The steady rest is a hydralic selfcentering, quite powerful. I quess the smartest way to do this, is to clamp the stock the stock in chuck, and then use somkind of adjusteble collet with a center at the end of stock, so I can use the center to cut out a surface for the steady rest without forcing the stock into any position, and after that clamp it in the rest and machine my center, then cut a surface for the chuck and steady rest for machining the other side. could this work ? I have no problem getting a center at this time, but the shaft will come out like a banana when unclamping it.

[mc-motorsports]

Tram the shaft to the chuck face, this will put your shaft on the same center as the spindle bearings centered between the point where the shaft is being held by the lathe chuck and where it's being held by the steady rest.

Learned that one from a German trained ID/OD grinder. He was one of the best machinists I've worked with.

MC

[ejparrott]

100 is quite a bit smaller than what we usually do but we have a method for centering shafts.

We have a 16" four jaw chuck, in the back of which we have (lightly) pressed in a tophat bush, the back of which has a large cone in. We 'clamp' this to the end of the shaft, and put the tailstock into the center. You can then clock he shaft true, or to best advantage, and then skim a steady band. If you then set the steady to this, you can then remove the tailstock, remove the chuck, face the shaft end, then centre. You can now remove the steady and turn as normal off the tailstock.