So I decided to scrape my gibs....

[PriddyShiddy]

I spent the weekend scraping my new Z gib. the scraping part was much easier than expected, but after I was done with the back I needed to remove about .02" to make it fit. A few short cuts later it was ruined and now I have to order another tomorrow.

However I DID scrape the old gib very carefully adjusting the taper and when reinstalled my head nod was COMPLETELY GONE. the backlash stayed about the same, but the adjustment is completely used up with only the top adjustment ring being in the top of the gib.

Next I decided to try the X & Y which blew me out the water. There is almost NO CONTACT. it seems like the adjustment screws are too low on the gib and its only pushing the "heal" into the very bottom of the dovetails.



???

I scraped the line where is running... 6 times... no change. gave up in the X and pulled the Y. EXACT SAME THING. tried scraping both, even tried moving the gib over so that the adjustment screws were on the flat and it didn't change anything.

The only thing I can think of is pulling the table and scraping the dovetail... and thats out of the freaking question.

any thoughts?

consequently- scraping the gibs lowered my X from .0043 to .0019 and my Y from .0039 to .0026. the movement was noticeably smoother but just kills me that the contact is so small. I'm completely stumped.

[Johann ohnesorg]

Given that you had a good starting experience with scraping on the Z-axis I guess you´re hooked now.

Since your gib only rides on a burr you have to find a way to cut the burr in the dovetails sharp corner. You could break a sawblade into pieces and line them up parallel so you can saw down in the dovetails corner. It´s a pita but it works. Or you can get a knife file to reach in down there. First of all, inspect with a torchlight. Take a piece of toilet paper and run it in the dovetail. You´ll see and feel where it grabs due to the burr.
Since you already pulled the gibs and the slides, measure the ways with two precision pins and a micrometer to see if they are parallel. If not correct. On some of these machines, you´ll find that not only the gibs are not parallel, they are not even in the same plane. In this case, blue up the seating surface of the base and see if it is straight or what is the deal with it. Mine was hollow in the middle, this leads to a crooked way when you bolt it down for milling it parallel. You bent the base, cut the new dovetails parallel, open the fixtures and presto, it bends back into a banana.
So first mill or file/scrape the base lower side flat, turn around, then remill the dovetails on top. You can maybe shim the base, too so it sits flat before cutting it.
Don´t forget to mill a side of the base straight in the same setup as you mill the dovetail. You may have to index in the casting with a DI later on and then a reference surface comes very handy. While you have the casting on the mill also make sure to mill the seating surfaces for the leadscrews rectangular to the dovetails. They are off more often than they are straight. No problem with a normal ACME screw but in case you think CNC sooner or later the screws may bind if the seating surfaces are not perpendicular. It´s easy now to do it, it will not even cost you 10 minutes.

Bad thing about scraping in a Sieg machine or one of it´s clones is that they used 55° dovetail angle. I measured mine, decided that I want to go down the "fix me" road but not with 55° but with standard 60°. In effect, I remilled the ways to 60 degrees, cut the whole shebang in one setup so everything is straight and parallel and then, from a known straight surface that is parallel to within 0,001" I started scraping. This works pretty fast. The 60° remove about 1/16" from the dovetails width. To compensate, I made gibs that are 1/16th thicker, a huge increase in stiffness, too.
This will remarkeably stiffen up the machine. You can bend the original gibs easily by applying too much force and you have to do it only once. Even using the lock down screws can do this. Not a problem with my thicker gibs anymore.

Another thing: You´ll be surprised what you´ll find under the bondo. Keep a little bit of cast iron rod nearby. You can cut a thread on it and glue in plugs with loctite 248 in locations where our chinese friends drilled holes that were not right and filled them with Bondo.

Cheers,
Johann

[PriddyShiddy]

unfortunately it is unlikely I will have the down time available to be able to re-machine the mill. it seems that their design is just flawed. the adjustment screws are below the level that they should be to apply pressure on the face of the gib instead of just the "heel". if I had .015 backlash I would likely justify that much work, but since it performs this swell as is its going to stay for now.

I am shocked that I'm able to run 100ipm and hold tolerances within a few thou as is, but I'm just going to keep making parts and turn this thing into a high precision drill press when I can move next year and have space for a Tormach.

thanks for all the info!

seems like it would be easier just to install linear rails and bearings though

[Johann ohnesorg]

Linear rails, too are a joke if you put them on crooked surfaces. Doesn´t help at all, it´s like putting lipstick on a pig.
The only thing that helps is to get the geometry straight and parallel, no matter if you use rails or dovetails. It´s surprising what the X2 and it´s clones will do with the factory setup. It´s amazing what will happen if you really blueprint and finish them.

Cheers,
Johann