My travel is 570mm absolute max

Then chances are that a 550 mm scale will be terminally unhappy at some point !

I don’t recall working with any glass scale having much excess travel over its rated capacity.

You could use a 550 scale if you put hard stops in place to restrict the travel to within the scale capacity – but chances are that you will then get a job that is just within the machine physical capacity, but just outside the scale capacity.

If a 600 scale will fit in the space available, just get the safe length – can’t see there being much difference in price. If you intend to use reference marks on the scale it would be as well to know where these are on the scale travel – some have one mark in the middle of the scale, but others have a mark close to each end of travel. If the latter, it may be necessary to bias the scale one way when you mount it such that it is “safe” from overtravel damage but still allows the reference mark to be traversed at one end.

Nigel B.

I remembered that I have an un-mounted Chinese glass scale in the garage – a “Jing” branded item that is the Z axis scale for my mill that I really should get around to fitting ! I guess that I haven’t got around to fitting the Z scale over a year after fitting the X & Y units confirms what others said earlier about the “necessity” of a Z axis readout !

This scale has a rated measuring length of 400 mm & I have just measured a total mechanical travel of 420 mm dead stop to dead stop so in line with the values given to you by your seller. I would be happy running at 5mm over nominal – less so at 20 mm over, which would need very careful ( accurate !  ) installation to avoid damage.

HTH

Nigel B.

Have a look at M DRO they do kits which will fit your mill.

DRO Milling Kits

I have one for my 16V mill . They will supply all brackets and fitting instructions and they are very helpful about setting it up. I haven’t had any problems with my one and it is over three old at least and very acurate.

David