View Full Version : straightning a shaft

08-16-2003, 12:42 AM
I have a cross slide screw shaft on asurface grinder that is bent on the outer end past where the threading ends. Apparently someone tried to lift this machine by the handle and bent the shaft. This causes the handle on this machine to wobble. I have the shaft out of the machine and have mounted between centers and determined where it is bent but so far have not been able to get it perfectly straight. I wondered what methods have been tried by others to straighten something like this?

08-16-2003, 01:02 AM
You could make a straightener like the ones they use to straighten shafts on lawn mowers. The straightener is a collar that would mount over the screw section for a couple of inches and then have a bored out section over the bent section of the screw. The wall thickness needs to be thick enough to be drilled and tapped for screws that will be used to straighten the shaft. Screws are at 90 degrees apart and at several positions along the bores section. Tighten the screws on the high point will move the shaft back where you want it. This is a terrible description, sorry about that but this type of straightener works. Wish I could draw a sketch and post it.

Hope this helps.


08-16-2003, 01:06 AM
Use a hydraulic press to straighten it between two supports. Take your time - less is more!

08-16-2003, 01:22 AM
To add to Thrud's advice......rig up a dial indicator under the bent area. Rotate the shaft in the supports to determine the high/low spot. Overbend slightly to compensate for springback.

Repeat the procedure until it's straight enough to satisfy your needs.

I want to emphasize the use of an instrument like the dial indicator to accurately determine the low spot. If you try to find that spot by eye you'll be "chasing" straightness for hours and may make the situation worse by introducing more bends into the shaft.

08-16-2003, 02:04 AM
It might be easier to identify the bent area by rolling the shaft on a very flat surface. Try to find some heavy tube or pipe that closely fits over the shaft so the straightening force is concentrated on the bent area.

I hope the bend isn't in an area where the shaft is threaded. It's been my experience that parts get just a little longer when straightened. Metal stretches more easily than it compresses.


08-16-2003, 10:52 PM
By using the indicator you can also determine how much to bend i.e. if you bend it .020 and it's not enough try .030 and vice versa. You can get very close and not have to chase as much.

08-17-2003, 08:45 PM
Use two vee blocks to determine the location of the bend. Only streighten where it is bent and this will mean locating the bend on the shaft using a dial indicator on the end. Once you have it located, locate were the dial indicator indicates lowest point on the bent end and mark this as you point of press. Place the shaft in a press, either arbor or hydralic with the mark up and the shaft between two more vee blocks or similar and start your streightening process. Place a second dial indicator on the press to give you some idea as to the amount of deflection you are useing. This is the only way to accuratley streighten the shaft. Work back and forth between the two sets of blocks and indicators. Until the shaft is streightened.

08-17-2003, 10:01 PM
I used the press method with a dial indicator set up and was able to get the shaft straight. Thanks everyone for the help.