Bridgeport 9X42 Table needs to be Re-Ground

[Janderso]

I would like to know if any of you have had this done, if so how much does it cost?
I love this old beast (1970 step pulley system) and I don't mind putting some money in her to freshen up the precision.
I have heard of Chicago Grinding and they suggested someone in the West Coast to save on shipping costs. I have not found anyone. There are several companies that look down at this kind of work I recently found out.
Thank you very much.

 

[benmychree]

I was told that regrinding (only) the table top can cause the whole table to distort, this by a machinery rebuilder in Berkley Ca. who is no longer in business. There is or at least was a rebuilder in Fresno; also a good question to ask Richard King on this forum.

 

[Janderso]

Calling Richard King.
I have read good results from regrinding, that's interesting. I was told also by Chicago Grinding and Machine, the flatness depends on the underside as they lay the table on a flat surface of the grinder and go to town. "As long as the table has not been butchered up on the bottom it should clean-up good".
To Chicago and back it's almost $400 and 15-20 days in transit.

 

[benmychree]

Rich is teaching a scraping class in Vacaville right now; I forwarded this thread to him at his e mail address.

 

[tertiaryjim]

You havent given any information of the table top condition or any pictures.
If it's warped even a small amount on top it will be warped on the bottom also. Hey, its one big hunk of iron.
So, the dovetails need to be checked and if you repair those of the table the knee must also be done.
Some warp can be peen'ed out to help it. Don't peen working surfaces. If it's not bad it can be scraped.
Rich is the person to talk to.

 

[Richard King 2]

99.9 % of Bridgeport tables and other brand machines, that are off the old machines. (older then 15 years, as I have never rebuild newer then that) the Bridgeport table is bent or bowed high in the middle. I used to think it was because they were so long and unsupported. But a friend and who used to teach Engineering at Penn State I think it was, Archie Chiba who used to be a frequent advisor on PM, told me they bow because when the machinist vise is tightened so many times over years the T slots stretch the metal. Or he called it "peen" the table..I only thought peening was from the hammer. At first I thought that was BS, but as I worked on them and asked other rebuilders I discovered he was right (unlike what some think I listen and test others ideas. As my Dad used to say "when you stop leaning your dead"!

I have tested peening the bottom of Bridgeport tables and have successfully bent them back by peening the bottom ribs and middle sections of the table advoiding the dovetail castings. The 20 or so tables I have tested average about .008" bow.

I have experimented on how to test them. after you stone or sometimes file the table top because the T-stots are raised up or burred up or some bozo (Tom Lipton says that a lot as he is one of my students this week) some bozo dropped or scratched the table. Then set it on 4 1-2-4 blocks on the flat ways on a granite or cast iron surface plate. Then using a height gage / .0005" indicator make all 4 corners the same height height. You set the 1 2 3 blocks at the Airey points (approx. 30% from each end) and tap the blocks with a rubber hammer to move them on the curvature to raise and lower the table corners and then check the entire table.

More later as I need to get to class. Gluing Rulon (Turcite) today and the students start there projects. Oh, and John thanks for the scrapers. I hope you can make it to the class in Oakland. John is a great machinist and good rebuilder who helps me in the Oakland classes. Rich

PS: There is super grind shop the CA rebuilders use between SF and LA called Shafer Grinding. They do great work and are reasonably priced.

 

[Janderso]

First of all, I am new to machining. I don't know the questions to ask. Regarding accuracy, I have no illusions, this machine and table are well used but, the head is quiet, the back gears are also running with no objections. The table has milling marks, drilled holes and has no flaking left except on the outboard edges. I assumed out of ignorance a regrind would bring it back to plum. For the price I paid I am very happy with what I can accomplish with this analog piece of equipment, the backlash is not bad, I do not have a DRO.
I appreciate the information, especially excited about a west coast shop!!

 

[tq60]

Is the table not true or ugly?

If re grinding because ugly pause...


If because not flat above postings are new and interesting things to consider.

Richard always brings interesting things to cause us to think more.

One must consider their planned operations and needs before attempting to bend the table true or regrind and hope it stays true after grinding, read what Richard has posted relating to these things as he is the expert there.

If one is primarily doing small work in a vice and the limited movement of table varies much less than expected tolerances than spend time and effort on other things for now until the need for true table warrants it.

If due to ugly...

Ours had a few places where an end mill shifted hole cutting and cut into the table and that was deemed ugly.

Went over to the bench grinder with a magnet and collected a bit of ground up iron then cleaned table with acetone and mixed a small batch of epoxy then added the iron and made a paste.

Filled the holes then later made flat to table.

Hard to find them now and supports things on table fine.



Sent from my SAMSUNG-SGH-I337Z using Tapatalk

 

[Janderso]

First of all, I am frustrated with tramming. The table has so many milling gouges and drill holes I’m not sure how to do it. I trammed the vice to get square and 90 degrees to the head.
I guess I could lay a precision ground straight edge on the table to make an effort.
I don’t plan on doing any precision milling but I need to have confidence a pass from one side of a piece produces the same depth.
Squaring up stock, I haven’t tried that yet, I have a 2x2 piece of cold rolled stock a foot long, I could cut it to 2 inches and make a squaring effort.
Ugly or not true? Ugly! True? Not sure yet.

 

[Eddyde]

First of all, I am frustrated with tramming. The table has so many milling gouges and drill holes I’m not sure how to do it. I trammed the vice to get square and 90 degrees to the head.
I guess I could lay a precision ground straight edge on the table to make an effort.
I don’t plan on doing any precision milling but I need to have confidence a pass from one side of a piece produces the same depth.
Squaring up stock, I haven’t tried that yet, I have a 2x2 piece of cold rolled stock a foot long, I could cut it to 2 inches and make a squaring effort.
Ugly or not true? Ugly! True? Not sure yet.

You can use a trued brake rotor as a tramming aid, just lay it on the table roughly centered on the spindle and you can sweep the indicator all the way around.