Way Lapping

I have a RF 45 and have it apart, working on reducing backlash. I thought I'd investigate lapping the ways while I'm at it. I see some old pages on the web that refer to a procedure that was produced by IH (who is now gone). Can anyone point to a copy of that procedure or send me a copy?
Also, I'm not familiar with scraping. I see some think it is better than lapping. Would be interested in knowing something about that as well. thanks, rex

Lapping and grinding make for a smooth surface.
The mating part should be scraped if the one or both of the parts move and are expected to move with ongoing accuracy and precision.

Think about it this way. When you slice the Thanksgiving turkey and the juice runs off the cutting board onto the counter. Because the surface is smooth the juice (fat) runs onto the floor and you get in trouble. Now if the cutting board was place one of the rubber floor mats from your truck the juice (fat) would be trapped in the grooves of the mat. You'd still be in trouble but the reason is different.

Scraping provides very very very small dimples or pockets which trap oil and lubricate the surfaces. Two precision ground surfaces wouldn't even slide as the oil would be squeezed out.

The trick is machine tool geometry. I'm in the appreciation and learning mode for machine tool geometry and am only beginning to understand it. The difficulty is making every surface parallel or perpendicular to every other surface/axis as might be appropriate. Understanding the relationships, measuring the irregularities/error and doing something (hopefully the correct thing) about it is critical.

As long as you have her apart, then you may as well have a look at her especially if she was giving you trouble. However, unless you are brave and a adventuresome gambler many would like a coach on their first scraping job. You might solicit input from a local HM Member who may have an opinion.

Please understand that their opinion may be that I have no idea what I'm talking about.
I'd have to second that opinion.
Go eat turkey!

Daryl
MN

Backlash doesn't involve ways, it involves screws and nuts. What is it you are trying to fix by lapping or scraping? Are the ways worn unevenly?

Dear Rex,

Forget the lapping of ways. Diesel engine injector nozzles get lapped to their respective bodies. Not lathe way surfaces. Daryl is right. If you want to do anything to a lathe bed ways, the only way is by hand scraping and for that you will need a number of years practice (and tons of patience) to get right. If I were you, I'd approach the whole lathe rebuild in a way that you end up with a machine that is in a better condition than before you took it to bits.

For your lathe, inspect the ways and remove any burrs that you may observe on any of the slides. By burrs, I mean little knocks or dings that the casting edges or surfaces may have received. This you can carefully remove with a file in the localised area of the dimple that is higher than the average height of the slide surface. Then obtain some engineers marking blue and put a thin layer on one of the mating slide parts, normally the longer slide. Then with no oil, put the mating slide onto the way and give it a full length slide over the way, remove the casting and have a look at the un-blued slide. you will see that some of the blue would have transferred to the slide that was not blued. A normal contact pattern is around 60 to 70 %. You will also be able to see if there are any high spots or if the average bearing surface is good or not. A lot of what I'm saying has to do with developing a feel for things, which you will come to appreciate with time.

If everything looks good, clean the slides and put them together with a thin film of oil and slide the castings together and feel if they bind or slide over the full length that they are intended to work on. For this test you will have to put the jib's back into the slide and adjust them to ensure that you can slide them without any noticeable rocking, binding or seizure. For all intents and purposes, if the slides do not bind and feel good, they are good and you should not need to do anything else, to have a lathe that will give you years of good service.

For what you describe as backlash, this I presume is with the cross and compound slide threads and nuts. These are normally acme threads. If the acme threads have worn to any degree, they will look like normal threads with sharp points and these you will have to renew to reduce the backlash. If they are not severely worn, screw the respective nut onto the thread and feel if there are is any noticeable end play. End play may be noticeable in one part of the thread while at other parts of the thread it feels good. This is because the slide that the thread and nut assembly drives was used in this position the most and therefore has the most wear.

But don't despair, my Southbend 9 inch model C lathe cross slide has about 20 thou backlash and it works just fine. I just keep it in mind and snug up the slides if doing anything that may end up causing some chatter. I still turn to one thou accuracy, which is acceptable to me.

Re-assemble your lathe and I'm sure that you will have a better machine than what you started with. If anything, it will be cleaner and you may even want to paint her to make her look better. How about posting some photos of your lathe rebuild project. We all like the before and after pictures. Here is an after picture of my SB9C. Enjoy, Geoffrey.

>For your lathe, inspect the ways

Good advice...but an RF 45 is a square column mill.

Dear Chris,

Sorry about that. I Googled RF-45 and saw that your machine is indeed a milling machine. It looks quite sturdy.

Nevertheless, the advice I have given applies to all machines. Of course the testing and adjustment of any machine can only be done after it has been re-assembled. In many machine shops around the world, machinists work around imperfections in their machines, by making allowances for the known imperfections. It is however nice to have a perfect machine to work on, but believe me, there are not many of them floating around. Even with new machines, which are most probably out of your and my price range, as hobby machinists.

If I were you, I'd re-assemble the machine and do some checks on alignment and squareness and with these readings, decide on what to do to reduce any bad points. On a milling machine, the slide nuts can be adjusted to reduce wear that has taken place on the threaded rods and the ways can be adjusted to a good feel over their range of travel. Just tramming of the vertical head can do wonders to the finish of machined parts.

I really hope that you enjoy re-building your milling machine. Geoffrey.