Need Help!- Using a manual bridgeport without a DRO

[ccarlsen]

I have been working with a Bridgeport mill for several years now, equipped with a Acu-Rite III DRO. This mill is in one of the more public labs on my campus, meaning that many of the people using should not even be allowed to hold a dull hack saw. The x-axis glass scale has stopped functioning (the shield on it is practically non-existent), and despite a complete wipe down with ethanol and q-tips, has refused to come back to life.

There is a project with a fast approaching deadline that requires several ~36 inch long pieces to be milled. I have been using the scales on the handles to do all of the x-axis positioning, counting each rotation. Is there some better method to measure travel other than just counting rotations and reading the knob gauge? Facing both sides of a 36 inch piece requires 182.5 rotations using a 1/2 inch tool, I feel like this is prone to too much human error.

Additionally, the handles seem to have some play in them, meaning that when I change directions I loose ~0.050 inches. Is there a way to compensate for this and/or remove this play? It was no problem with a DRO so I never paid it any attention.

[HawkJET]

Originally Posted by ccarlsen Is there some better method to measure travel other than just counting rotations and reading the knob gauge?

Each turn is .200" and you can use a tape measure to get within the proper turn and then adjust from there with the dials.

Originally Posted by ccarlsen ... when I change directions I loose ~0.050 inches. Is there a way to compensate for this and/or remove this play?

Always creep up on your dimension from the same direction. Or, measure the actual backlash on that area of the screw and compensate.

Back in the day, we didn't have these new fangled electronics toys and had to do all the thinking ourselves.

[keebler303]

I normally put layout fluid on my stock and mark all the important dimensions, then I know I am on the right turn and just have to worry about the reading on the dial.

Matt

[aka.apprentice]

Originally Posted by HawkJET Each turn is .200" and you can use a tape measure to get within the proper turn and then adjust from there with the dials. Always creep up on your dimension from the same direction. Or, measure the actual backlash on that area of the screw and compensate. Back in the day, we didn't have these new fangled electronics toys and had to do all the thinking ourselves.

Lol, I'm not that old but I wasn't allowed to even plug in the DRO while I was learning. I know you're probably finished by now, but just adding to what HawkJET said-

Even if you don't have a tape measure you should only have to count the dial the first time. (Assuming you've got a repeatable setup where your reference edge on the x axis never changes.) After you've counted your 182.5 rotations and finished your first cut, mark the table on the x axis and on your dial. (A line on the static and dynamic surface) Whether you use a piece of tape, wax pen, permanent pen or dry erase is up to you. Now you can just machine close to the pen mark within 1 revolution, and finish your cut by going to the number marked on your dial.

Hope that makes sense, not the greatest at explaining things. =)