Checking a bridgeport table

I recently had the table ground on a surface grinder and it looks great, but I know they didn't grind the ways.

To check their work on my 4' x 3' surface plate, I just need to put the table on the plate and raise it up using 123 blocks so I can run an indicator under under the surface as well as over the ways. Also I need to put pins in the ways and use a micromiter to measure the distance there.

Is that the right way to do it?

Put it on 3 points Tee Slots down. Measure in 30% from both ends placing 2 on he edge or side even from the end.
Then place the 3 rd one directly in the middle spanning the t-stot at 30 % in. Then use a height gage to measure both sides. The use 2 -5/8"x 2" dowel pin sand mic the dove tails. You can screw in long allen cap screws ..2 on both ends to pick up the table with a crane or 2 guys can do it. A fast way to see if they ground the table correctly is to set the table T slots down on bare granite table and "hinge" it or pivot it and if they ground it right it will pivot from both ends at the 30% mark from both ends. Rich

Awesome, thank you very much for the info!

SirRage said:

I recently had the table ground on a surface grinder and it looks great, but I know they didn't grind the ways.

To check their work on my 4' x 3' surface plate, I just need to put the table on the plate and raise it up using 123 blocks so I can run an indicator under under the surface as well as over the ways. Also I need to put pins in the ways and use a micromiter to measure the distance there.

Is that the right way to do it?

Click to expand...

Oh boy, this one is going to be fun

Seriously. Support it at the airy points using 3 blocks. 2 on one end and one on the other end. that will allow the table to assume its natural shape, will not force any twist or bow. I assume that you calibrate all your blocks and the surface plate so you know what range errors you can ignore. If you truly trust your surface plate you can check your table surface just by bluing it up. When you put the table face down, bang on it all around with your fist or a dead blow hammer and listen for any clanking or any sounds that is not just hollow thud like hitting the granite itself. If you find that it is not flat see if you can get feeler gages in under the edges. Hinge the part, it should turn on the airy points (about 30% in). Rub it around turn it over see what you get. If you get bad coverage you can go many ways to find out what is going on. Hoisting it on the blocks and sweeping the bottom is just one of them. Hopefully the grinding shop knew not to just suck the table on the magnet and make it pretty.

If your table is not quite flat, you can scrape it flat, if it is way out, it needs to be machined. Anything more than 5 thou is more than one would want to scrape off a table. Once you have the surface flat you can turn to the ways. Measure the flats from the surface plate, use dowels and micrometers to measure the dovetails. make sure the dowels fit in the dovetails and the radius close to the inscribed circle of the equilateral triangle formed by mirroring the dovetails. (sounds complex but measure the height, assume 60 degree dovetails divide the height by 3 and multiply it by 2 that is the approximate pin diameter). You need two exact size pins.


good luck

dee
;-D

Richard King said:

Put it on 3 points Tee Slots down. Measure in 30% from both ends placing 2 on he edge or side even from the end.
Then place the 3 rd one directly in the middle spanning the t-stot at 30 % in. Then use a height gage to measure both sides. The use 2 -5/8"x 2" dowel pin sand mic the dove tails. You can screw in long allen cap screws ..2 on both ends to pick up the table with a crane or 2 guys can do it. A fast way to see if they ground the table correctly is to set the table T slots down on bare granite table and "hinge" it or pivot it and if they ground it right it will pivot from both ends at the 30% mark from both ends. Rich

Click to expand...

You were more concise..and typed faster...

+1 on everything..

dee
;-D