J-Head worn ways?

I have acquired a one owner 1960's vintage J-head and am working on getting it set up. I've trammed in the table to within 0.0005" each way when the table is at the middle of its range. I placed a dial indicator directly under the spindle and ran the table to it's extents. I figured this would tell me if the table was running flat. The indicator shows a 0.003" slope from front down to back, and 0.007" high on left and .002" low on the right. Need some help on what is causing this and how to fix it? The table is a 9x48.

Most likely the table ways are worn more in the center than at the ends. First check the top of the table for flatness. Put a pair of gage blocks or matched 1-2-3 blocks on the ends of the table. Stretch a thin wire tautly over the blocks and measure the gap along the table. Take the table off the machine and do the same on the underside. If you have access to a surface plate big enough for the table, use a dial indicator.

The fix is to rescrape the ways of the the table flat as well as the matting ways on the saddle.

This may be more than you wish to tackle in which case you just learn to live with it.

Tom

What Tom said.

Yours actually isn't all that bad. It can still be "worth it" to try to get 80% improvement for 20% the effort of a full rebuild, but we are talking a few thou, not a few tenths of a thou. A SIP-Genevoise, nor even a Gorton, it was never. A BirdPort's HEAD can flex more than that table-error you have just clocked. Lots more.

How many different points did you clock with different Z height anyway? The knees sag, too, and not so politely as to be uniform at it, all positions.

Beyond that? Plan to shim your work now and then and JF Deal with what you have. Most work doean't run full-traverse, any axis, in any case, so it works well-enough

The 48" tables are thinner than heftier mills and get out of dead-straight too easily. Fixing any mill's table when it does much of that is a non-trivial exercise as you have to work top surface and underside ways more than once. Corrections to each simply tend to move the other as you go.

You've ever seen a dog chase it's own tail? OK.. now price that exercise at shop rates - your own with scraper. Those of a grind shop. Or both!

2CW

Just a thought, but was your knee locked when you were doing the test? There could be rock in the knee that causes movement in the table/saddle as the weight of the table goes from one side to the other.

Thermite brings up an important part of this... what are the tolerances that you want to keep? If you are happy with a wavy finish that could be 9 thou off, then you dont need to do anything.

Just so that you know what you could be getting yourself into, if you sent us your knee, saddle, table, and gibs, its about $3k to grind and hand scrape your ways in. If you sent us the mill to do it, you would be looking at that cost plus the labor cost to disassemble and re-assemble it all. When we do way work, we get less than 5 tenths play in both the X and Y axis. That cost also gets your table re-ground. Just so that you know what sort of $$ you could find yourself getting into, if you sent it to a shop to get ground and scraped.

Jon
H&W Machine Repair

You have a decision make.

Do nothing and accept what you get. A point here, a good tool maker could use that machine as it and make perfectly acceptable tools. Its rare for a tool shop not to have worn machines.

Second, you could start to rebuild it. As is the usual case, you get something done and then you aren't satisfied and so you start to rebuild another part of it. If there is that much wear on the slides then there is a good possibility that the feed screws and nuts are worn. Then there are the spindle bearings. And on and on until the machine is completely rebuild, everything up to snuff. Or you could send the machine in for a complete rebuild. I have heard numbers in the range of $7,000 for this.

Your choice.

Tom

I only had a few min to play with it last night. I rechecked the machine's level and it had settled a bit since placing it. re-leveled and recheck. I did not have the knee locked during the measurements and I'm only measuring at the height for my currently slated project.
Re-leveling brought the right side of the table back near zero and I found the left side starts to go high about 8" from the end. I think this is due to the fact that the power feed wiring was too short to allow full movement to the right thus, not wearing it evenly. Makes sense with what you are all saying. Didn't check the Y. I'll live with it. Just means I need to check everything before each project run to shim and understand my tolerances. Thanks for the help

Jrock338 said:

I'll live with it. Just means I need to check everything before each project run to shim and understand my tolerances. Thanks for the help

Click to expand...

Sanity check. THIS is what one does.

Ninety-percent or so of mill hands who have any serious amount of TIME on mills were using mills we did not OWN. Not all that assured it would even be the SAME mill, two jobs in a row. "Company machine", IOW.

Hardly ever did one enjoy anything close to "as new, no wear".

As this machine IS your own? "One and only", even? It won't be as hard.

In the fullness of time, you'll "know its ways", pun intended, and adapt to it. Much akin to how one adapts to driving a certain run of bad road without going into the ditches.

Judging by the fact it's 1960 machine I would not think you are doing high precision work. You hardly ever make parts that require the full X/Y travel so doubt even shimming your work will be necessary.

BTW, level is not as critical on a B/P as say a lathe. I purposely ran mine out a little so any coolant would run to drain hole on one end.

True, I really don't have any project slated that requires high precision, and yes, by buying an old Bridgeport, I accepted that I might not be able to do everything as precise as I may wish. I agree, with the 48" table, I probably can avoid the higher area. I do map all the "ways" of my machines and this one will be no different. I'll probably pick up a granite block to check my work after the process. Thanks for the help.

With any worn machine, just KNOWING what is worn and how much is going to enable you to make good parts IMO. Rebuilding it just gives you one less thing to monitor, but it isn't always necessary.

There's all those old adages about "good machinists don't blame the machine," and such, and they all boil down to the data you've collected, and being able to apply it to your skill-set.

On a machine like this is it a good idea to do most work at the ends of the table? To slow wear in the center and add wear on the ends to help even it all out?

I remember when I was an apprentice and my Dad would have me move the vise on the Bridgeport on the table and not always in the middle. Also when we surface ground he had me clamp the part on each side so the machine wore more even.

Those Bridgeport tables are bent more then wear. Archie Chiba (professor) first told me about that and at first I didn't believe him, but the table tee slots get stretched when you tighten the vise down. Sometimes they are bent .010" and I figure Primitive Pete must have used a cheater bar on his Tee Nuts.