View Full Version : Gib Fitting Question (Bridgeport)
02-03-2008, 12:24 PM
A bit of noticeable table slop is now apparent on my Bridgy. It's not as old as some on here - 1985 step pulley - but the slop on both X & Y can't be adjusted out on the gib strips anymore as the adjusting screws are fully home.
Having taken both gibs out, it looks they have been coated with what I assume is Turcite in the past, as both sliding surfaces have a thin layer (around 1/16") of a dull greyish green polymer material bonded on to them.
This has subsequently had oil grooves hand-cut into the surface.
So time to make or buy some new gibs I think.
My question involves fitting these for those who have done this in the past. I've been told that a new blank gib will require both cutting to length, machining of the slot for the adjustment screw head, machining of oil grooves, and possibly scraping for the final fit.
Can anyone confirm the correct procedure for any of the above please?
For reference, it is a 1986 step-pulley J-head built by Bridgeport Textron in the UK, rather than the US (according to serial number format).
Cross Posting Warning: Also posted on PM in the Bridgeport Forum
02-03-2008, 12:43 PM
I was in the same boat except that I had enough wear in the knee ways that I could not adjust for full travel under even tension. My gib had been turcited as well.
If you are going to go to all the trouble to scrape in a new gib, you might just as well just buy more turcite (available in a whole range of thicknesses) and replace what you have. You need to clean the gib thoroughly, then soak in lacquer thinner to remove any remaining oil. Rub it to a surface plate to see if it is flat, as it should be and if not, scrape it back in. Start by scraping the back flat and then do the face. Even if it rubs flat, the scraped surface will help with adhesion. Turcite is adhered with a special adhesive made by a company called Shamban (product name escapes me). You can imagine how hard it may be to get good adhesion on teflon, so don't skimp here. For years, the adhesive had .005 glass beads in it to insure that it had a consistent film thickness when you applied it. I read somewhere that they dispensed with that. You will need to be able to clamp the gib to your surface plate turcite side down on waxed paper to insure even thickness. The turcite face is then scraped in to fit. I have not done mine yet, but I am told it scrapes nicely. Turcite contains teflon and is impregnated with bronze bits to prevent crushing as teflon is quite soft. Actually, Turcite is a brand with Turcite B being the right product for sliding way surfaces. Rulon also makes a similar product although the product number escapes me right now.
Both products are something you may want to approach a machine tool rebuilder about as you only need a small piece of the Turcite and a tiny bit of the two part adhesive. Even then, be prepared to pay. The turcite is not cheap. I got a quote for a piece of 1/32" thick stuff big enough for that small gib from a place here in the states and I think they still wanted $50 US.
An easier approach is to cut a shim from plastic shim stock of the appropriate thickness and fit it to the back of the gib. Cut it with the same screw head slot as the gib, and it will travel with the gib as it should. In my case, the turcite had worn thin and pulled away at one end so stripping it and then scraping the gib back flat and replacing the turcite (along with completely rescraping the knee ways) was the right solution.
Edit-- When I suggested new turcite followed by scraping it in, I meant scraping it to fit the mating dovetail way surface. This is what is required whether you use turcite, or a new, un-fitted gib.
02-03-2008, 03:39 PM
Paul, thanks for that info, very useful.
However, as the Turcite strips are usually thicker than required, I have a concern as to how to machine it closer to size (pre-scraping) if either the X or Y gib is out of the mill when you need to use it.
02-03-2008, 04:23 PM
I use Garlock Multifil 426, very similar to Turcite, and it is very easy to scrape.You can tell the glue side because water will wet it, the other side it beads up.
When I was redoing the carriage on my Monarch I tried power scraping Multifil. That lasted about 2 strokes. Used a hand scraper, was very easy to scrape.
02-03-2008, 04:55 PM
[QUOTE=Peter Neill]A bit of noticeable table slop is now apparent on my Bridgy. It's not as old as some on here - 1985 step pulley - but the slop on both X & Y can't be adjusted out on the gib strips anymore as the adjusting screws are fully home. BINGO!!!!
THE QUICK & DIRTY FIX , ROLL A PC. OF 12 GAGE WIRE AT LEAST 3/16 LONG & DROP IN, REPLACE ADJUSTING SCREWS,THIS WILL GIVE MORE TRAVEL , OR MAKE BRASS PLUGS.!!
02-03-2008, 06:08 PM
No flames yet...I don't understand what you are talking about, Larry. What are you supposed to do with this 3/16" piece of #12 wire?
Turcite supposedly scrapes quite nicely....much easier than cast iron such that you could easily scrape back to dimension even if you had a lot to remove by hand.
One thing you will want to make for yourself is what the fellow who tought me to scrape called a "gib board". Gibs are too hard to hold still while scraping. A gib board is just a board big enough to stay under its own weight, or which is clampable. You then use a fewsmall wood screws to create a border around the perimeter of the gib....just enugh to keep it from sliding around and to give you something to work against as you scrape in alternating directions.