Saturday, September 11, 2010

Truing a Puller

One of my workshop's operating principles is "you can never have too many pullers". So when I saw this 8" puller on special at Princess Auto I made sure I got myself one.

These inexpensive pullers from offshore do give you a lot of metal for your money, but they tend to come up a bit short on precision, and are likely to need a little attention before they'll work as well as they ought to.

The shortcoming with 3-jaw pullers that I keep seeing is in the uniformity of the lengths of the jaws. When the lengths are uneven, the tool sets up crookedly. The defect doesn't render the puller useless, but it does make it clumsy to set up (and pullers are clumsy enough things to set up when they're perfect) and it does impair the puller's effectiveness -- the puller's force is off at an angle to the subject axis; that's not helpful.

To check the jaw length evenness, dismount the jaws and rack them up on a close-fitting bolt or length of threaded rod. Any length unevenness will be obvious.

I think I'll have to ask you to trust me on this, but that near-side jaw at the lower right is shorter than the other two. The puller will set up crookedly. This puller is actually not too bad in this regard; I have a 6" puller that was much worse. (Why the factory cannot or will not amend its methodology to correct this is beyond me.)

You need to also examine the jaws at the other end, and assemble the jaws using the other hole and examine both ends. In this case, the other end was good enough not to need attention; there's just this one short jaw that wants grinding to even it out with the others.

Here's the rig I came up with for grinding puller jaws:

That angle grinder has an M8 threaded hole on either side for a handle, so it was a simple matter to make this prop arrangement that presents the wheel at an angle suitable for grinding the hook-faces of puller jaws. The next photo shows the process in action.

This is not precision machine shop work by any stretch of the imagination; it's rough, nasty, 'by guess and by gosh' work. You'll find it a bumpy ride as particles lodge is the wheel now and then and kick the work. Check your progress often, and don't expect a pretty outcome. The result pictured below is where I stopped and said "good enough".

As I said, it's not pretty. The sheer size of these jaws made this job more difficult than others I've done, but I'll have a better puller for having done this.

The final photograph is of the jaws of a 6" puller that had very uneven jaw lengths, much worse than this one's. On that puller, one jaw was much longer than the other two, to the point where I would have seriously weakened the other jaws had I ground them to align with the long jaw.

I got around that by fashioning a shim that I could crimp onto the face of the long jaw. It worked well. I pulled a brake drum with this unit the other week and the puller set up nice and straight. It certainly wouldn't have prior to the grinding and the addition of the shim.

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