Assessing machine wear

[Matthew DavenhillParticipant @matthewdavenhill31115]

[Matthew DavenhillParticipant @matthewdavenhill31115]

point

hi all,

A straightt forward question I hope! I’m stripping a Bridgeport and it’s seen a shift or two! On each of the machines ways there seems to be what I assume are machined datum surfaces either side of the dove tail. So for the question ! How do I assess the wear and what kit do I need?

[David George 1Participant @davidgeorge1]

Hi Mathew what model Bridgeport do you have and what expectations do you have as it is a can of worms depending what you intend the machine to do. I have refurbished a few in my working life but I had access to a large 8 foot by 4 foot granite surface plate a granite square and lots of lifting and machining equipment. The most wear on the slides were usually X axis worn in the middle so tight on the ends and loose in the middle and on the Y axis the same but not so bad but the adjustment gib strip was usually worn out. Let me know if you want any detailed information or you could send me a PM for contact details to phone me. Where are you based?

David

[SillyOldDufferModerator @sillyoldduffer]

I'd suggest evaluating the machine before stripping it. By moving the slides and other functions normally and abnormally (e.g. by leaning on the table & head etc), you may be able to feel problems, and a DTI will reveal fine misalignments and unwanted movement.

Once you've confirmed the problem can't be corrected by an adjustment, then it's time to take things apart and have a look. My experience is very limited, but – for example – rather than elaborately measuring a dovetail to confirm it's dimensionally correct, I'd look for wear with a straight-edge. As wear is unlikely to be even, it can often be spotted by reference end-to-end . As David George said 'The most wear on the slides were usually X axis worn in the middle so tight on the ends and loose in the middle'. This sort of error can be confirmed by shining a torch on the back of a straight-edge. Then the size of the error can be measured if need be.

As an self-trained beginner I found taking accurate measurements to be much more difficult than I expected. Also, when measuring a machine-tool, it's easy to be misled as to what the actual cause of a problem is. It it ain't bust don't fix it.

My experience of the forum is that's excels when you ask specific questions and can provide photos. Chaps like David know their stuff and are pure gold. Don't be afraid to ask.

Dave

[JonParticipant @jon]

Think i know what you mean Mathew.

If it has datum points some quality machines do have them will need precision bars off them with some form of traversing dti. Unless bars clocked up you wont be able to measure any runout or wear of the dovetails.

General quick easy way of testing for slide wear is try and lift the bed or slides at the point where it wears the most. If gets tight at extremes its worn.

Personally i would bite the bullet its a quality machine not a disposable variety and have it precison ground, finer the finish the better ala DSG.

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