Comparing worm shaft depth with three wire method

4 Attachment(s)

Hi All
When machining worm shaft for the rotary table modification I am currently working on. I had an issue on how to check that I had machined to correct depth as I had no gauge to check fit before removing from the lathe. As I had removed original worm shaft from table, I decided to use the 3 wire method to check correct depth was achieved. I didn't have any thread wire gauges so decided to bend a piece of 5/32" rod as this fitted in the Vee-form nicely and was high enough to measure over the top of rod. I produced Mod 2 form tool using a tool and cutter grinder so was reasonably confident profile would be correct so the only thing I needed to worry about was the depth. I know this method is used to normally check the effective diameter and thread fit but this worked and enabled me to compare original worm depth to new worm. The photos below will hopefully clarify this method.

Attachment 31507
Wire gauge bent from 5/32" rod

Attachment 31508
Wire gauge in place ready to be measured with caliper

Attachment 31509
Another view of wire gauge in place for clarification
The gauge is a good tight fit over worm and is slightly sprung to keep in place and ensure all three wires are snug in the vee-form of worm

Attachment 31510
Measuring over the wires.
Both shafts measured the same across the wires and when the new shaft assembly was test fitted there was no play and moved table smoothly.

Thank you for taking the time to read
The Home Engineer

It is great that you had the old one with which to compare - assuming the reason for making a new one didn't involve a poor fit of the old worm gear.
No tables or books, any handy wire, and a bit of ingenuity!

Well done.

I really like that self holding wire measuring idea, it beats my 3 wires in a cork or plasticine method. These simple tips are little gems.
Thanks.

Just this morning I was trying to measure an 8 TPI/Morse taper adapter that I was cutting to compare to a wood lathe spindle nose with the 3 wire method, and discovered I'm not near coordinated enough to pull that off. Thanks for the idea, I'll give it a try next time.