I have an opportunity to purchase a milling machine that is within my budget and will possibly with a little sweat equity be a decent machine for my "out of control" hobby shop.The machine has Meehanite castings, DRO and X axis power feed as well as a one shot lub system
How would one go about repairing a three inch diameter cutter mark that is in the center of a 9X42 offshore mill table that is .050 deep.
This machine also has .30 backlash on the X axis. Any tricks to repair or improve this?
Are there any sites that have any details on hand scraping some of the original hand scraping marks are worn off so it likely has some wear?
I have not purchased this machine yet , but might consider it if these flaws can be corrected.
My 2 cents worth: I almost always use a vice with my mill. The only time I have used the actual top surface to hold material is when I have worked on some large 1/4 inch tooling plates. In all cases, an oops like you describe would not matter.
I have used JB WELD to repair a cast steel vice that had a bunch of drilling oops in it. None were where pressure was applied and was used for cosmetic appearances.
My suggestion is to ignore the problem unless the sight of it bothers you.
I wouldn't worry about either issue. Stone the table top to rempve any burrs and forget about it. Backlash shouldn't be a problem either with a DRO. You might want to create a little bit of "drag" with the table locks if it wants to move under heavy cuts. All of this is considering thet the price is right. Randy
I guess this miller is a Bridgeport clone, and so I'm not familiar with any anti-backlash adjustments it may have because I've never owned one, but some other milling machines have adjustable feed screw nuts. The setup is a pair of bronze nuts that are threaded on their OD as well as their ID. They screw into either end of a collar which is anchored to the saddle casting (in the case of the X-axis). With the feed screw running through both nuts, backlash is adjusted out by unscrewing one or both of the nuts in the collar by a small amount. This has the effect of changing the overall thread pitch of the nut/collar assembly which reduces backlash. Its very similar to the way jam nuts work, except that you have more control over their separation from each other.
Anyway, I'd crawl under the thing and inspect the feed nut assembly for some type of adjustment like described above.
As for the gouge in the table, I *think* Moglice
in a formulation that is suitable for such repairs. Moglice is a castable liquid way liner material. Essentially like Paul's suggestion of using JB Weld but more purpose-made for the job.
Bridgeport's scheme is the nuts are smooth cylinders on the OD, and fit in a close-fitting bore in the yoke. The nuts can be split with a bandsaw into two full cylinders (not lengthwise). There is a wide-head screw that will squeeze the two pieces together, and a locking screw that keeps the big one from moving. You tighten up the big screw until the leadscrew binds at the ends, where the wear is least, then back it off a hair. The nuts are bronze, and hard as hell, so when the wear becomes significant, it means the screw is worn, too.
The X axis adjustment can be made with a flashlight and long screwdriver without taking the machine apart. Newer machines come with the nut already split.
If it was mine, and it bothered me enough, I'd bore it deeper, then plug it with a quality piece of cast iron, then refinish the surface *very* carefully. That wouldn't work if it breaks into the T slots. Or live with it.
That is a non-issue. Machine tools have backlash----it's a fact of life (unless they have ball screws). You learn to use the machines, regardless of the amount. It's what separates a machinist from a wannabe. Besides, .030" is hardly backlash. New machines often have that much.
I too would not worry about the cut in the bed as small parts can be put elsewhere on the table while large parts won't worry about the hole. The slop is something that you need to look at. If the dial moves in and out then it is just a matter of taking up the slop in the bearings with the adjustment system on the shaft. If the dial doesn't move then the nut underneath is either worn (easy to replace) or needs it's adjustment done, depending upon the machine. From the description of the scraping, I'd suspect that the machine is pretty well worn and will need some TLC to bring it back to specs. I'd check it out with a dial test indicator to find out what else is wrong with the machine.
-- Why do penguins walk so far to get to their nesting grounds?
They're both just epoxy. Not much point to filling holes in a cast iron table with a soft glue, except for looks, or to avoid catching chips.
JB "Weld" ought to be boycotted anyway for fraudulent trademarking and the general abuse of the English language. And "SolderSeal" (another glue colored to look like metal) while we're at it. Some guys just want to believe.
If you really mean .30" backlash, there's something seriously wrong with the machine. If you instead mean .030", that's not bad. There's always backlash, you just have to learn how to compensate for and work with it.
It's been pointed out that all new machine tools (even Monarch lathes and Moore jig borers) are made with used machine tools.
I'm curious, though. Did even the quality machine tools from years past get shipped new with backlash as much as much as 0.030"?
All but one of the axes of my modest collection of lathes, mills and grinders has less than 0.015" even though the youngest is nearly 30 years old and some of them look pretty well used and none of them are top tier..
In some cases the JB Weld or preferably better epoxy fix might be ok but this approach is definitely better. Especially on a large hole like he's talking about.
Agreed. I think it's rather funny when everybody gets concerned with the backlash on a machine. Every machine will have backlash in some amount. They have to if you're going to be able to move it. If there's no play anywhere then there's no way to move it. Balls screws do help but that's only useful in CNC where the motor locks the screw.
My Sidney lathe has at least 0.070" backlash but it doesn't concern me (at least till the cross feed nut finally gives up the ghost).
Agreed. If it really is 0.300" backlash, that is more than one turn of the leadscrew, which means that at least *some* of that backlash has to be somewhere other than the fit of the nut to the leadscrew. I could see something like that *possibly* happening if the screws mounting the nut to the saddle are loose. If so, tighten them and re-check. Also, the leadscrew may be loose in the bearings at the end of the table, allowing end float. That should be controlled by a nut between the bearings and the crank.
However, I suspect that it is more a case of reading "30" on the dial when checking for backlash and thinking that it represents 1.000" full turn. That would really be only 0.030", as the dial is either
0.100" for a full turn, or 0.200" for a full turn, depending on the leadscrew pitch.
When I got my well used 12x24" Clausing lathe, the cross-feed leadscrew had a backlash of 0.070" (with 0.100" being a full turn of the leadscrew. In that case, both the nut and the leadscrew were badly worn. Instead of the leadscrew looking something like this (Acme thread) (View with a fixed pitch font, like Courier. Proportional pitch fonts will distort the image, because the spaces are a different width than the '_', '/' and '' characters.
Un-worn leadscrew (thread crests should join the sides, but not with ASCII drawing): _ _ _ _ _ _ _ _ _ _ _/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \
Badly worn leadscrew:
If the "flaking" is worn off the ways (not really the scraping, but special deeper scrapes designed to make scattered reservoirs for waylube, to allow it to be distributed on the mating ways as the machine moves), then it is likely that the leadscrew and nut have already been replaced once -- so you could have 0.030" backlash in the replaced leadscrew and nut, and *lots* of wear on the ways. On my Series-I Bridgeport, the ways are chrome plated and *ground* flat, not scraped. The flaking looks at though it might have been put in with an angle grinder at a shallow angle. Chrome ways are too hard for normal hand scraping.
Note that if you try to tighten the nut so as to eliminate backlash in the middle of a worn leadscrew, you won't be able to run the leadscrew to the ends, as the nut will be too tight in the relatively unworn section.
Seriously, backlash is not a concern, not if the machine is otherwise sound. I've run only one machine that lacks it, my Graziano, on the cross slide, and only because it has a loaded nut. Regardless, I run it like it has backlash, which is the habit one must acquire to run (manual) machine tools successfully.
I just checked the backlash on the table of my Bridgeport, purchased new in '77. .059", and I am not concerned in the least. I know the machine still runs well, and I can rely on the screw for positioning. It's not the machine, but how you apply it that counts. Some day the screw and nut assembly may require replacement, but not right now.
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