PDA

View Full Version : Face plate issue



bearing
11-05-2012, 05:32 AM
This face plate came with the SB 9, it is a craftsman face plate, it does screw go on right up to the backstop however, there are still a few threads left and it about 030 out of line according to the dial indicator.
Is this ok to use on my SB 9 with a few threads still showing and is there anyway i can straighten it out.

http://i478.photobucket.com/albums/rr144/bluearc5/lathe/lathe11-5-12002.jpg
http://i478.photobucket.com/albums/rr144/bluearc5/lathe/lathe11-5-12001.jpg

thanks

SGW
11-05-2012, 05:53 AM
As long as it seats against the back of the faceplate you're fine. Threads showing in the front are irrelevant.

First, make sure the threads are clean before you measure.

To true it up, put some hi-spot blue on the back of the faceplate where it contacts the spindle shoulder and see how much contact area you are getting. Scrape that surface until you get uniform contact all around when the faceplate is screwed on. Then see what your runout is. If there still is runout, take a skim cut across the face.

This might be a good place for a carbide toolbit to ensure it stays sharp for the entire cut. There is also the problem of wildly changing surface speed from the o.d. to the center, and carbide may be more forgiving of the variation.

rohart
11-05-2012, 06:31 AM
It looks to me as if you're talking about the gap at the back between the faceplate and the register of the spindle. That is not too healthy. Anything that screws on to the spindle should smack right up against the register.

Since there seems to be no obstruction at the front of the through hole in the faceplate it looks as though the thread starts to jam before it has screwed onto the spinldle properly.

What does it feel like as you thread it on ? Does it jam up slowly, or does it just stop dead ? If you force it round a little more, does it go ? I think you have to have a close look at the internal thread in the faceplate for dings. If you find anything you could try to scrape it out.

It's also possible that the internal thread is either the wrong pitch, was not threaded deep enough or was threaded with the cutter at an angle so the flanks of the thread are off. With either of these errors you will have to remove some of the thread to make your faceplate screw on properly.

If you decide you want to use this faceplate despite the problem, I would mount it with a washed behind it so more of the front portion of the thread is accessible and just turn off some of the thread. You only need to remove as much of the working portion of thread as you have a gap at the back, and removing thread that wasn't going to engage anyway will not reduce the fit at all.

quadrod
11-05-2012, 06:38 AM
Can we see a picture of the back of the face plate off the lathe? I'm wondering if there is no relief cut into the threads to match the non threaded portion of the spindle before the shoulder.

topct
11-05-2012, 06:59 AM
This is how I would fix it. The spacer is made in one setup. Bore, face, and part off. Screw the face plate on backwards, then you can not only face off the register surface, but if the internal threads need to be machined away or the bore enlarged the face of the plate is square with the spindle.

You can remove a bit of material and try the plate. Using the spacer you can always put it back on if more work is needed. When the plate will screw on all the way with a solid bump when it gets tight, then you can take a facing cut off the front and the diameter.

http://img.photobucket.com/albums/v78/topct/IMG_0140.jpg

J Tiers
11-05-2012, 08:33 AM
We might have got off the rails here...........


This face plate came with the SB 9, it is a craftsman face plate, it does screw go on right up to the backstop

Apparently it DOES touch the shoulder, and so SGW has the answer.

It's very normal to have to skim the front of a new-to-the-machine faceplate to get it to run true. 0.030 is a little more than I'd like, so I would do the suggested testing and scraping of the back surface of the faceplate where it touches the spindle shoulder, which may correct it.

if no hi-spot blue, just put "Majic Marker" ink on the back of the faceplate hub surface, and put the plate solidly on the spindle. when it is taken off, any place that touched the ink will be rubbed off. Those are the high spots.

if the rubbing of is all around, and fairly well distributed, you are as good as it gets. if in one spot, then scrape or (ugh) file off a little in that area, and repeat. Do again until the ink shows that the contact is all around.

be sure no grit or whatever gets in the threads or stays on the hub contact surface when you are trying the fit, or on mating surfaces at any time when mounting any sort of spindle tooling (chucks, faceplate, centers, whatever).

After that you probably will find the error less. Then you can take the light skim cut on the face to just "clean up" the entire surface. After that, it should be good for years unless something drastic changes.