Need suggestions/coaching with making a lathe gib

[Curtis]

Hello guys;

The original cross-slide gib on my Chinese 9 X 20 (yes, I know that these are not good machine tools, but it is what I have) is too narrow for the slot it fits into. So, I had ordered a piece of brass 3/8" thick and long and wide enough to machine the new gib from (I have a Taig mill). This is what the various forums recommend as gib material, but when machined this brass warps very badly. The result was a tapered length of brass strip with an obvious bow to it. I tried to straighten it with my press, but could only get it within 3 or 4 thou of straight and even then it is still tapered. So my adventure with trying brass for a gib went sour. So my questions are these:
1) what material do you guys suggest for a new gib?
2) how do you hold it flat while being milled? I have a tooling plate and can clamp from the edge, but there will be no down-pressure from
these clamps. Would I have to buy and use toe-clamps? (they are very expensive).
3) How to prevent warping with the next material that I try to make the gibs from? Would use of hot-rolled steel or leaded steel eliminate the
warping problem or is this something I am going to have to live with in trying to make the new gib?

Thanks in advance for any answers to my problem.

 

[Terrywerm]

I am no expert on making gibs, but I wanted to address a comment you made in your post relating to your 9 x 20 lathe. Don't discount your lathe because of where it was made. Like you said, it is what you have, and it will do a fine job on just about anything you tackle. Remember, 90% of a machined part is in the operator, not the machine itself. Since you are making improvements to your Chinese lathe, I expect that in time it will be far better than when you got it and will do a right respectable job.

With all of that said, the gibs on my lathe are all steel, not brass, but I don't see where either one would not work. As for tips for machining your new ones, I do not have any ideas right off the top of my head other than to clamp a piece of flat stock larger than you need to the table, then machine what you can reach, 'inside' of your clamps down to the proper thickness. Once that is done, remove your stock and cut it to length and width. If the piece bows a bit, I would not worry too much, as it would simply provide some springiness to the gib, keeping your crossslide tight all the time.

Anybody else have something to chime in with??

 

[DAN_IN_MN]

Search for " Stress Relief " on the internet. Might be the answer you're looking for.

 

[4GSR]

The easiest way to hold a gib while machining is by bolting/screwing it down to a fixture plate as I've done several times over the years.

Now keeping it flat takes a lots of patients and time. Just stress relieving the material alone is not enough. First thing I do is to get it to near net shape leaving about .030"-.060" stock. Don't do all your cutting on one side, swap sides between cuts. After the roughing stage, start taking lighter cuts .030, .015, last cut around .005". Again swap sides between cuts. This will keep the gib fairly straight when finished. Also use sharp cutting tools. Dull tooling will cause gib to warp severely! After this the rest is scraping and fitting. The screw holes are filled with Epoxy or liquid metal.

 

[Curtis]

I am no expert on making gibs, but I wanted to address a comment you made in your post relating to your 9 x 20 lathe. Don't discount your lathe because of where it was made. Like you said, it is what you have, and it will do a fine job on just about anything you tackle. Remember, 90% of a machined part is in the operator, not the machine itself. Since you are making improvements to your Chinese lathe, I expect that in time it will be far better than when you got it and will do a right respectable job.

With all of that said, the gibs on my lathe are all steel, not brass, but I don't see where either one would not work. As for tips for machining your new ones, I do not have any ideas right off the top of my head other than to clamp a piece of flat stock larger than you need to the table, then machine what you can reach, 'inside' of your clamps down to the proper thickness. Once that is done, remove your stock and cut it to length and width. If the piece bows a bit, I would not worry too much, as it would simply provide some springiness to the gib, keeping your crossslide tight all the time.

Anybody else have something to chime in with??

Terry; Thanks for the encouragement! I have to admit that I had not thought of using a larger piece of stock and clamping outside the area needed :thinking: and then machine the area inside the clamps. I had to laugh at my own inability to "think outside the box" on this one. Thanks for your help, it is much appreciated.

Curtis

 

[4GSR]

Here's my fixture for cutting the angle sides on a gib.

 

[Curtis]

Search for " Stress Relief " on the internet. Might be the answer you're looking for.

Dan, I did think of this, and per info that I found on the net about stress relief I tried annealing the brass at 500 degrees F. in my oven for a couple of hours during an earlier attempt at making this gib. The problem with brass, as I found out is that it work hardens as you machine it. So, even when annealed it soon warps again from the machining process. It is amazing to watch this stuff (C360 brass) bow as you are running an end mill over it.

 

[4GSR]

C36000 half hard brass will not stress relief. All you doing to it is changing the temper to it if the temperature is high enough. And machining it just adds stresses to it, too!

 

[Curtis]

The easiest way to hold a gib while machining is by bolting/screwing it down to a fixture plate as I've done several times over the years.

Now keeping it flat takes a lots of patients and time. Just stress relieving the material alone is not enough. First thing I do is to get it to near net shape leaving about .030"-.060" stock. Don't do all your cutting on one side, swap sides between cuts. After the roughing stage, start taking lighter cuts .030, .015, last cut around .005". Again swap sides between cuts. This will keep the gib fairly straight when finished. Also use sharp cutting tools. Dull tooling will cause gib to warp severely! After this the rest is scraping and fitting. The screw holes are filled with Epoxy or liquid metal.

Ken;

In that pic I see what look like small holes (black spots) - are these holes for the screws that you are talking about using to hold the gib material in place for machining? If that seems like a silly question, please excuse my newbie obtuseness; I just want to make sure. I had not thought of holes going through the sides of the gib strip material to hold it into place for machining, but as long as the holes do not interfere with the gibs' function in the end, then why not? Seems like a real good idea to me and thanks for the tip.

 

[Curtis]

Here's my fixture for cutting the angle sides on a gib.

Ken; how much excess material do you allow for machining the stock down to the finished size in a gib? For example, the cross slide gib I need to make is about .210" in width and (from memory now) about .375" in height. Would .250" thick HRS that is say, .500" wide be large enough to allow for machining to finished size that I quoted, or do I need to go bigger on stock size? Thanks, btw for outlining the process of cutting and mentioning turning the stock- flipping from one side to another for the machining. I did not do this and I guess that tells you how much I lack experience. My thanks to all you guys who chipped in with suggestions and your knowledge. I very much appreciate it!