Centring Spindle

I need to position the spindle on my miller in the centre of a bearing on a small petrol engine, its about 15mm inner race, the plan is then to remove this bearing so that I can bore down in-line to another bearing housing so that it will take a roller bearing instead of a brass bush.

I have never used wigglers before but am wondering if this is something that they can be used for?

Thanks in advance

Paul.

Hi Paul,

I have not used wigglers but I know they are used to position the spindle axis with reference to an edge. If you have a DRO on the X and Y axis of your mill you can use the wiggler. Position the wiggler approximately in the centre of the bearing. Move the X axis so that the wiggler is indicating it is aligned with say the left hand side of the hole. set the X axis zero at this point. Now move the x axis so the wiggler is aligned on the right hand side of the hole. Note the X axis reading. Divide this reading by 2. Now move the table so the X axis displays this value. You are now centred on the X axis. Repeat this on the Y axis. You do not need to know the diameter of the end of the wiggler for this to work. Some DRO's have a centre function which removes the need to divide the reading by 2. If a finger type DTI you could mount it on the spindle and turn the spindle by hand positioning one axis at a time so the reading is the same on both sides of the hole. Another way would be to make a piece of metal that one end fits in the collet chuck of the mill and the other fits the hole you are trying to align to. before the crank case is clamped down have the end of this piece of metal in the hole to position the crank case. Now clamp the crankcase down to the table. Raise the Z axis so that the piece of metal is withdrawn from the hole. now lower the Z axis to confirm the piece of metal enters the hole to confirm the crankcase did not move when clamped down. I think the DTI method would be the most accurate.

 

Les.

Les

You just beat me to it.

 

I would just add that it might be better to remove the bearing and set up from the bore in the casting itself.

I would personally forget the wiggler and stick with a finger type DTI gauge (if you have one)

 

Also make certain that you have "trammed" the mill, to be sure the head is square to the table.

 

Phil

Hi Paul,

You only need to compare two readings at a a time with the DTI method. I also agree with Phil about setting up to the bearing housing. Also I think I would set up to the brass bush housing rather than the ball bearing housing. Whichever method you use you need to have a face that you are sure is perpendicular to the crankshaft axis that sits on the mill table.

 

Les.

 

Paul,

 

If you try to use Les's first method on a mill without a DRO, relying on the feedscrew dials, you will almost certainly get an unacceptable error because of backlash in the feedscrews.

 

David