Options for worn ways repair

jmhoying

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My newly purchased 1979 Millport (Bridgeport J-head clone) has a lot of slop in the table. I've tightened the gibs but still get a fair amount of rotating on the center line motion when pushing or pulling crossways on the end of the table. I can make the problem disappear by tightening the x and y locks. Like most mills that are well used, the problem is most noticeable in the central area of movement.
I guess I already know that the answer to my question is "complete scraping job", but I was wondering if there is a method that will tighten up the table without all the investment in specialty tools and the learning curve for scraping. I know that is the only way to bring my Millport (Bridgeport J-head clone) back to new standards is scraping, but at this time, I don't have to have 100% precision in the ways. I haven't checked them for wear, but would there be any benefit to truing up the gibs only at this time?

Thanks,
Jack
Fort Loramie, Ohio
 
Most of the time the top of the knee is the worst as the ways are shorter then the table and smaller wears faster. If you want to check the knee for a quickie cheap appraisal,get a couple of 5/8 dowel pins or some drill rod (if you have to you could use cold roll, but mic it and mark with Sharpy a 3:00 and 9:00 side and always use the same way, will explain how next) about 2" long. Crank the saddle out as far as you can with gib loose toward the back. Clean and stone the ways to knock off any burrs. Then lay one pine on each side of the top of the front of the knee opposite each other and use a micrometer to measure the distance from out side of pins and record.

Then push the pins in toward saddle say 3" and measure again, and again. Then crank the saddle to the front and clean and measure the other side or behind the knee. If you don't have 8 to 9 mic I think that's the size use a dial caliber. The table is probably bent and worn. Many rebuilders will cut the T-Slots to relieve the peen-ing or stretching the metal in the T-Slots. I have never done this, but believe it can be an issue. I have turned a table over one time and peened the bottom of the table in the middle area with a rounded punch and have straightened them. I have seen some Bridgeport's table bent .012" The bent table will make it bind up on the ends. Take the table off to check it and I am hesitant to tell you to peen it if you don't have the plate to lay the table of to check it. I suppose you could use a 36" steel rule or a straight sheered piece of sheet metal and use a feeler gage to judge the table top. I would just lay a camel back up there, but I have several sizes. Measue the knee and table and let me know. To see if we can make a few suggestions. Rich
 
Richard,
Thanks very much for your detailed response. I measured the ways on the top of the knee tonight and it looks like the center area is about .011 smaller than the front and back. Is this considered a bad case?
Jack
 
Richard,
Thanks very much for your detailed response. I measured the ways on the top of the knee tonight and it looks like the center area is about .011 smaller than the front and back. Is this considered a bad case?
Jack

Its terrible. Probably a combination of the flats being lower allowing the pin to roll deeper into the dovetail and the dovetail is worn too. If you have a surface gage like a Starrett (56a) and attach a dial indicator on the rod swivel and measure the flat of the way to the top clearance or the surface on top of the dovetail. C to A and B to C Do the test along the the flat the same as you did with the pins. I hope my crude sketch of the top of the knee works.
............a..................... b .............
_____\------i_______i-------/______
__c __\............................/__c____
l..................................................l

there isn't an easy fix. It will need to be machined and scraped or scraped. It's late will write more later. Have the Uncles funeral tomorrow. So will probably not write till Friday. Rich
 
A few questions on how one would interpret these results if you don't mind.

What sort tolerances would one expect of a new machine? Would these measurements be dead on?

If .011 is terrible, what sort of measurement would be acceptable? I know acceptable depends on the tolerances one is trying to work to, but could we get some kind of ballpark region of "not too bad"?

Thanks much
brian
 
I've scraped in .011" plus thousands on a old knee slide on a ancient Brown & Sharpe mill in my younger years. Used a cast iron surface plate that must have weighted 150 lbs. It wasn't easy. At least at the time, we had a Biax scraper that helped. Dad and I took turns scraping, finally got it to about 70-80% over most of the areas. There were hard spots in the cast iron from all the years of pounding from the saddle. After that ordeal, the saddle was put up on a shaper a planed. Talked about a lesson learned!!!!

Not to speak in Richards place, you ask, What is considered acceptable".

I my words anything is acceptable if it is doing a satisfactory job in the work expected from the machine. If it's not, then its time to evaluate and determine what the cause is. If it is wear, as indicated, how much? Next, put a game plan together on how to correct/improve the wear to when the machine is put back in operation it will do satisfactory work.

Does not mean the wear in the slides has to be perfect within 50 millionths in flatness as Richard is known to teach and do. (No offense Richard) I bet for most of us HSM, if It was within .002-.003" in flatness (in 12"?), it's good enough to last a lifetime for us. My 13" lathe has about .004" wear in the bed ways, but I can keep the taper in 18" to within .0015", which tickles the heck out of me, closer if I baby it.

I will say .011" is a bit much to live with or to fix by scraping.
 
Its terrible. Probably a combination of the flats being lower allowing the pin to roll deeper into the dovetail and the dovetail is worn too. If you have a surface gage like a Starrett (56a) and attach a dial indicator on the rod swivel and measure the flat of the way to the top clearance or the surface on top of the dovetail. C to A and B to C Do the test along the the flat the same as you did with the pins. I hope my crude sketch of the top of the knee works.
............a..................... b .............
_____\------i_______i-------/______
__c __\............................/__c____
l..................................................l

there isn't an easy fix. It will need to be machined and scraped or scraped. It's late will write more later. Have the Uncles funeral tomorrow. So will probably not write till Friday. Rich

I measured the distance (a-c and b-c). Both are right at .003 lower in the center. There are a few faint scrap marks on the front and back edges of the flats.

I assume that one of the "scraped" in the last sentence was supposed to read scrapped, which is scary to me. The part that really upsets me is that when I called the Craigslist seller, it turned out to be a classmate of my daughter, so I thought I could believe him when I said that I definitely didn't want a worn out mill. To be fair, I think he was sort of a hack machinist who didn't know any better (which puts a lot of the blame on me for not investigating better). The unit wasn't powered up, so I didn't start noticing problems until I got it home. An expensive lesson learned, that's for sure. That being said, I had contacted the seller early on when I found other issues (gear on power x feed, brake shoes, etc) and he gave me some of the purchase price back to buy parts. Now, I'd sell it back to him at a loss just to wash my hand of it.

I have to agree with Ken's comment about not needing this to be "better than factory" perfect. I'm mainly using it for repair parts and such, but it still needs to be better than it is now.

Jack
 
Get them straight and aligned by scraping, then use turcite to make up what was removed...Tim
 
I have no experience in this but have read somewhere that a product called "Moglice" was developed for this sort of problem.
Anyone have any experience of this product?
 
Lets re-evaluate what we have read so far: It would HELP if we all had some photo's to look at, so we are not guessing. I am trying to help him figure out what to do as a professional point of view. I tell my students when I am rebuilding a machine and I find ways out more then .005" to get them machined as scraping off .011 and keep it square, parallel, flat, and the right amount of points when done take a lot of work and in my case, a ton of time. As a pro, time is money because I have no doubt quoted the machine before getting the job. You owners who have lots of time can spend 100's of hours and time is not money if it's a hobby. On average on all the Bridgeport or clones I average 40 to 60 hours for the rebuild of the ways including the column, knee, saddle and fitting a reground table to the saddle, all the gibs. The machine spec's are better then new at .0002" per foot and 20 PPI. (I would never scrape a Knee Milling machine to .00005") I get the table reground and this does not include rebuilding the head.
To understand what he has I had him measure the machine. It's difficult to help over the internet but this will take a while. Rich in the UK, we spent weeks getting him on track, not 2 posts. Jack you have to be patient and the others lets analyze everything before getting to excited please.

I had Jack measure the ways so I could give him professional advise as I have probably re-scraped over 400 + Bridgeport's in my 40+ years of re-scraping Bridgeport's. My brother and I would have contests on who could scrape one the fastest.

I first asked Jack to measure the using the dowel pin's then the surface gage. To me .011 is terrible but can be repaired. The double "scraped" was a typo this morning as I was under the gun to get to the church, but wanted to help you. You need to relax and let us help you figure this out before calling the former owner. I have seen machines with deep scores, worn .020 and the owner says it worked great as he was using it more for a drill press then a mill. If you look back in this forums past posts. You will see some imported new machines that were sold new and were off .012" Now that's terrible too.

You don't tell us what you paid for the machine, so we can't judge your price and the machine value. Last spring LQQQ, I apologize if I botched the name, but he bought a machine that had cardboard behind his gibs, the knee, column and head stock were from different machines. He as far as I know fixed his machine. His machine was a mess and also terrible.

OK lets get to helping him on his machine.

Next thing I would like you to do is to remove the rear saddle wiper and see if the gib can be moved back future. Many times the gib hits the aluminum wiper plate and it appears like it is out of adjustment. Next you have to tell me or us what your expecting from the machine when your done? Can you live with .002" slop in the gib clearance. Have you also checked your table? Is it sloppy too?

In order to scrape the knee you are going to have to buy some tools, a straight edge a hand scraper, a precision blade square, bluing, etc. Probably a minimum of $500.00 in tools if you are lucky to find good used ones. and probably $1000.00 to $2500.00 or more if you have to make or buy newer ones.. If you have more machines to rebuild in the future then the investment would be worth it. If not you may look for a local rebuilder to do the work for you.

If you need help posting some pictures call me and I can help. If you don't have a digital camera and cant afford one, take some regular pic's and mail them to me. Those digital camera's are really amazing and if you don't have one you can buy them reconditioned or new for cheap online. PM me or call me and i'll help you.

I will be at home tomorrow and if you want to call me, please do so. 651 338 8141. It is so much easier to understand from a phone call. Then we can write here so we keep everyone in the loop. Rich

I added some info to his first post.

My newly purchased 1979 Millport (Bridgeport J-head clone) has a lot of slop in the table (.003" low when checking off a clearance surface on top of the knee that has never seen any wear and was no doubt machined on the same setup as the flat and dovetail ways are worn low and from approx. .004" per side on the dove tail ways. or .004 + .004 + .003" = .011. All with in the .005" spec I say to use when thinking about scraping of machining.)

I've tightened the gibs but still get a fair amount of rotating on the center line motion when pushing or pulling crossways on the end of the table. I can make the problem disappear by tightening the x and y locks. Like most mills that are well used, the problem is most noticeable in the central area of movement. ( he has a situation where he can tighten the saddle gib and it will not "rotate" as he calls it. I would say to remove the slop, but when he moves the saddle to the front and back it will bind up. What to do? I would scrape the top of the knee as it can be done. It sounds like he has never scraped before, so it's "terrible" to be a first timer to scrape one this bad.)


I guess I already know that the answer to my question is "complete scraping job", but I was wondering if there is a method that will tighten up the table without all the investment in specialty tools and the learning curve for scraping. I know that is the only way to bring my Millport (Bridgeport J-head clone) back to new standards is scraping, but at this time, I don't have to have 100% precision in the ways. I haven't checked them for wear, but would there be any benefit to truing up the gibs only at this time?

Thanks,
Jack
Fort Loramie, Ohio

- - - Updated - - -

I have no experience in this but have read somewhere that a product called "Moglice" was developed for this sort of problem.
Anyone have any experience of this product?

I used to be a Moglice Rep and have used it many times. You need to have a precision surface to mold the Moglice to. His ways are worn and Moglice is used where Turcite / Rulon would ride against the scraped way. Moglice has a product called Score Ex, but would not be used in this area.
 
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