Need Help With Carriage Gib Installation Problem

Nogoingback said:
Ed, notice that the contact points for the spacers are higher than the bed contact surface. If I machined all those surfaces flat, I'd have to make the spacers longer, not shorter. If I did that, I'd have
to use shims to adjust since the designed in "adjustment" would be gone.

Look at the location of the spacer contact points: outboard of the bolts. When the bolt is tightened it has a tendency to tilt the gib, which tightens the gib on the bed. The notches in the spacers
are there to clear a step in the bottom of the carriage.
Click to expand...
See I was thinking the notches were down. I can remember having a heck of a time with them ... but that was way too many years ago to remember clearly!! Thinking about the notches being up, now I understand the adjustment.

What I was trying to say before was, I would not remove the spacer contact points completely, just remove enough so that they are even ... but after all wear is machine from the bed contact surface. You will want the spacer contact points machined parallel with the bed contact surface. And the spacers the same size ... or you will end up in the same boat with wear on one end.

A different twist on my thoughts above: The two spacer contact surfaces really should not have any wear (and it looks like original machining marks on both sides). Use those surfaces as a reference to machine out the wear on the bed contact surface. That will make all 3 surfaces parallel. Then you would have to determine how much to shorten the spacers. Because you did not take any material off the spacer contact points, you would still have the same level of adjustability (I think).

If you hold the gib (by hand) so that the unworn right side is flat to the bed (or surface plate), how much clearance is on the worn side? Maybe I missed that above.

Maybe Scott will have a new one laying around, LOL.
 
You're right Ed, the bed contact surface should be machined, and the spacer contact points machined to match. The problem is I need the design specs to know how to do it correctly. It's true that there
is no wear to the spacer contact surfaces, but I can't reliably use them since I don't know if either one was machined correctly in the beginning. I can ASSUME that the left hand one is correct,
but at this point I'd rather talk with Scott first. He's supposed to be available tomorrow. What I hope for is that he has access to the original design drawings, and is willing to dig it out for me, or that he knows how much clearance between gib and bed there should be. If I get that
number, I can work out the machining.

If I clamp the gib flat to the bed, I can slide a .004" feeler gauge between the bed and the (worn) end of the gib.

I did have them check stock for a new one. They don't have it and I believe that they don't
keep castings like this in stock. I know when I spoke with Scott previously about the spacers,
he told me that they don't stock them.
 
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Nogoingback said:
... no wear to the spacer contact surfaces, but I can't reliably use them since I don't know if either one was machined correctly in the beginning. I can ASSUME that the left hand one is correct...
Click to expand...
That is a good point.
Nogoingback said:
how much clearance between gib and bed there should be.
Click to expand...

That would be something I would like to know as well.
 
Spoke with Scott Logan this morning. He said that the parts are not available and the drawings no longer exist. His
suggestion was to machine with the goal of minimum clearance. I asked if .001" would be good to shoot for and
he said yes, though I'll need to take bed wear into account as well. So, I'll have to take some very careful measurements to see where I'm really at and do the math. I'll
plan on doing it so that I can use the spacers that I have. And I have to find someone with a grinder.
 
I'm coming to this party a little late and my brain is a bit fried from a rough day, but I think I'm reading that the height difference between the two outer contact points and the bed grip surface is what's required.

I went thru the Logan pile-o-parts, placed the casting face down on a plate and stacked 3 razor blades and a shim to try to get the height delta. When using an 0.022 shim while holding down the bolt points, pushing the shim sideways caused the shim to rotate along one edge of the bed contact surface, while using a 0.024 shim and pushing the shim sideways caused the upper shim to rotate off the other edge, so I'll call it 0.023 + 3 stacked razor blades (0.075 inch for three), for a ballpark height of 0.098 inch. There was a very slight ridge on the tapped side of the bed contact surface, but just barely detectable with my index finger.

Also, both of my spacers measured about 0.516 inch height.

I believe the part I'm measuring came off a model 210 carriage, which appears to be the same part. If you don't have a way to square up your casting, I can send this one your way. Send a PM with your address if you want to give it a try.
 
Thanks for checking Tom. Right now I'm out of town for work and can't compare your numbers with my part, though
the fact that your spacers are the same length as mine is helpful information. I haven't had a chance to talk with anyone
about getting the part ground yet, though I know of at least one local machine shop that might be able to do it. I would
be interested in borrowing your part to compare with mine, and very much appreciate the offer. I'll PM you.
 
I am not familiar with Logans but a few observations make me wonder why the fit of this part has to be better than it is now. That might not be wear showing on the part but rather some grinding marks from when the part was initially fitted at the factory.
The design does not provide for adjustment like other style gibs have. Normal forces during operation are against the top of V ways and there should be no pressure on the 'gib' in question. There is no obvious need for this part to maintain an accurate sliding contact with the underside of the front way. The rear of the carriage is different because it is much lighter and forces may tend to lift it. Hence an adjustable gib is provided back there (on my lathe). I apologize if I am missing something and should mind my own business.
 
expressline99 said:
I can probably measure mine if it would help?

Paul
Click to expand...

Thank you for the offer Paul. TomKro has shipped a spare part to me which I'm waiting for. I'm also going
to take some accurate measurements on my lathe, so with all of that I probably will work it out. If I still have any doubts, I'll let you know.
 
Tozguy said:
I am not familiar with Logans but a few observations make me wonder why the fit of this part has to be better than it is now. That might not be wear showing on the part but rather some grinding marks from when the part was initially fitted at the factory.
The design does not provide for adjustment like other style gibs have. Normal forces during operation are against the top of V ways and there should be no pressure on the 'gib' in question. There is no obvious need for this part to maintain an accurate sliding contact with the underside of the front way. The rear of the carriage is different because it is much lighter and forces may tend to lift it. Hence an adjustable gib is provided back there (on my lathe). I apologize if I am missing something and should mind my own business.
Click to expand...

You have no reason to apologize at all. I did consider just putting it back together the way it is since as you said,
the pressure on this part is minimal. But, if I did it would be a thorn in my side: I just wouldn't be happy leaving it that way. So, I plan on fixing it.

The pattern on the part is actually wear: the photo isn't that great but if you had the part in front of you I think you would agree. The design of the front gib actually does provide for a small amount of adjustment by tightening or loosening the screws that are accessed at the top of the carriage. If you look again at the part, you can see that
tightening the mounting screws "pivots" the gib slightly off the contact points under the spacers.
 
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