Give me a while and I'll pop the gib out of mine and measure it.

Rob

It turned out a while was a couple of days! Still, here are some pics of the measurement technique and the figures.

Here's the gib coming out. Not sure if you've got the screw or not so I've measured that too:

After a cleanup, here is the item in question on the surface plate:

A fair bit of wear on mine. Also, it's not straight, which complicated the measurement procedure as I had to press it flat against the surface plate to get a consistent measurement. Firstly, length (all measurements are imperial as my gauge blocks are imperial, as is most of my workshop… and this mill):

Neither end is particularly square so about 18" is as good as it gets. There are a couple of drill holes in mine. Leftovers from fabrication perhaps:

First hole is 0.5" from the thick end, second is 9" in. I don't think they do anything.

Width of the flat bearing surfaces was gauged with a vernier. The bevels dont rub on anything so I don't think this dimension has to be accurate to the thou. Both sides are 0.80":

For the crucial measurement of the taper, I blued up 3 areas each 6" apart, lightly scribed some lines in the blue spaced as accurately as I could judge off a ruler 6" apart. These are the three measurement positions. Pressing down hard on the gib to make sure it was in firm contact with the surface plate, I zeroed a DTI with a few thou of preload. Once I had a consistent reading at the scribe line, I found the thickness of gauge blocks to also zero the DTI:

Readings were 0.4405" about 1 inch from the thick end, 0.3670" at 6" further on, and 0.2940" at 12". I make that between 0.146"/ft and 0.147"/ft taper. If you're making one I'd make it a few thou thick and scrape it in to fit anyway.

The top and bottom edges of the gib are anything but flat, so precision just isn't possible here:

Above it's clamped to a 123 block, there's contact at the first and second measurement lines, and a 12 thou gap at the third:

So to measure the broad width taper I sandwiched it between two 123 blocks and did the best I could with the callipers:

At the three measurement lines the widths were 1.158", 1.107" and 1.044". Prob about 100thou per foot allowing for the 12 thou out of flatness of the bottom edge.

In cross section the two bevelled sides are 45degree bevels:

And finally, a pic of my notebook page, with the gib adjustment screw dimensions too:

Edited By RobCox on 09/04/2023 12:06:55

Hi Martin,

Yes, my notes were being written on the fly as I was doing the measurements, so they're not exactly, er, comprehensible. Being of a certain age I tend to be fluent in both metric and imperial and have few qualms about using the most convenient units for the measurement at hand, hence the weird dimension.

I was comparing the thickness of the gib with a selection of imperial gauge blocks, using a metric DTI. As the DTI was being used as a comparator it shouldn't have influenced what I wrote down, but for the thickest part of the gib the DTI wasn't zeroed but read +0.01mm. Had I selected some of the "tenths" gauge blocks I expect I could have zeroed it but if I had dropped the gauge block stack by 1 thou the DTI would have read -0.015mm.

So, a gauge block stack of 0.4410in was 0.01mm too tall, hence the notation. The value in the text in the posting above is correct, to the nearest half a thou, ie. 0.4405in.

When you make the gib I'd be interested in your fixturing as I could do with a new cross-slide gib on my lathe and one day may get round to making one!