# How to verify the QCGB is accurate?



## knifemaker (Mar 11, 2021)

I picked up 9C that was converted to an A. It didn't come with any of the SB literature but was nicely equipped so I brought it home.  I have used it a little but not to single point thread.  I would like to know if there is a way verify that the feed rates on the front of the gear box are accurate.  I know I could just make a thread and see the nut fits but wouldn't that only be true for that one combination?  Any ideas would be appreciated!


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## dpb (Mar 11, 2021)

You don’t need to cut a full thread.  Run a scratch pass a couple thou deep, or, put a sharpie in the tool holder, instead of a threading tool.
Run a pass, check with thread pitch gauge.


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## knifemaker (Mar 11, 2021)

A sharpie is an excellent idea and outside the box!  Easy to check them all with a quick wipe with acetone. Brilliant! Thanks


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## projectnut (Mar 11, 2021)

It might have been a bit of overkill, but I did exactly what you're proposing when I bought my Sheldon lathe a few years ago.  Just to be sure everything was working correctly I made half a dozen samples of different size threads.  In my case I started with 1" diameter 6061 round stock.  Here's a picture of the threads I turned.  I made a few additional blanks for other sizes, but never got around to threading them.


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## ErichKeane (Mar 11, 2021)

I would just do a scratch-pass on some stock, and use a thread pitch gauge to confirm.  Typically you should be doing that before you do any single point threading ANYWAY (that is, running a scratch pass, then using a  thread pitch gauge to confirm).


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## T Bredehoft (Mar 11, 2021)

Put the carriage in gear, motor off, place a 1" travel indicator to measure the distance the carriage travels in one revolution of the chuck.
Engage feed/half nut, set zero, rotate the chuck (once you have taken up the slack in the gear train.) Read the indicator, do the math. You;'ll know exactly how far the carriage  moves for each revolution of the chuck. If it's a short  distance rotate the chuck ten times, divide measurement by   10 for accuracy.

Just how close can you compare scratched lines on a turned piece?


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## SLK001 (Mar 11, 2021)

A screw pitch gauge - standard equipment in every machinist's tool box.


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## knifemaker (Mar 18, 2021)

Just a quick update.  After using a dial indicator and trying several different gear combos all looked good.  So I cut about a half dozen different threads and all were quite good.  I even swapped the 56 gear box gear with the 20 stud gear and got it to cut a very acceptable 1.25mm pitch thread.  The more I play with this lathe the more I like it.


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