# Spiral milling - Quorn quick-start thread on the mill



## Lo-Fi (May 18, 2020)

Evening all

I've been engaged in creating my own "dogmeat" cutter grinder using what I have available. It's loosely based on the Quorn - at least the wheel head will be as I quite like the idea of the threaded column for course height adjustment (and allowing rotation) and fine by slightly tilting with a couple of screws. 

The quick start thread is a problem: I only have what might be called a "mini lathe" (Myford) that doesn't have a bed long enough to get the bar in, let alone support with the tailstock. In any case, I'm not sure it would like gearing the carriage to produce a 2tpi thread... I'm not surprised it scared the bejesus out of people. 

I do have a Bridgeport and a dividing head with an auxiliary shaft, which means that with the addition of some gears (that I also had to make) I can spiral mill. It's something I've always wanted to do too, so time to get to it. I'll fill in the details and calculations more fully when my fingers have recovered from turning the handle 1200 times, but for the moment, here's a pic of a piece of 32mm silver steel having a 15mm pitch slot cut down most of its length:




Video to follow, I'll have to edit and YouTube it as its too large to upload. 

Really enjoyed this, the calculation and setup was super fun! The actual machining op was hard work as I couldn't use the table power feed. The ratio between the table and dividing head is 13.333:1, so way too big an ask for the feed motor or leadscrew. The only sane way to do it was drive from the handle on the dividing head and letting it drive the table. I'll be rigging a motor up to drive it at the head for future ops, I've literally worm the finger prints off fingers and thumbs! 

Anyway, thought I'd share. Time for a celebratory scotch!


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## jwmelvin (May 18, 2020)

That’s pretty neat. I recent got a BS-0 clone and saw in the manual about spiral milling with the larger models.


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## benmychree (May 18, 2020)

There is no need to do calculations, find a copy of Brown & Sharpe's book "Practical Treatise on Milling and Milling Machines"; in the back are tables of all possible spiral leads.  Cincinnati's book on milling also has them.   Only problem on doing it on the bridgeport is that there is no table swivel, so you are limited to end milling spirals.


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## Lo-Fi (May 18, 2020)

I have the book actually! Possibly on your recommendation from another thread. I find that actually running the calcs myself gives me a far better understanding. Useful when you just need to get the job done, but I'm not on the clock and I enjoy stuff that makes me think! Also _invaluable_ for double checking that my calcs are correct 



benmychree said:


> Only problem on doing it on the bridgeport is that there is no table swivel, so you are limited to end milling spirals.




You tilt the head on a vertical mill and run the cutter from the side  same as you would a spur gear. I end milled this as I wanted a square profile, but it's not the only way to do it. Agreed that tilting the head 80 something degrees isn't really practical for this application, but helical are under 45 degrees unless you're essentially cutting a worm shaft of something really exotic, so quite achievable. That's the next little challenge!


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## benmychree (May 18, 2020)

One thing I did on my B&S #2 universal was to make an extension handle to crank the dividing head; I saw a illustration of it in a B%S screw machine book, illustrating cranking the dividing head by hand while cutting spiral cams for screw machines, I have never seen one in any of their catalogs.


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## Lo-Fi (May 19, 2020)

That sounds most useful! I may motorise if I have to do this again, I've got a suitable  motor and control kit somewhere around. Helical gears ought to be OK driven by the table power feed as the gear ratio table > head is much lower for shallower helix angles.


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## Rex Walters (Jul 16, 2020)

Hey, this is really cool. Nice job.

I’m in the middle of building a Quorn from the Hemingway plans and kit. Thank heaven the column arrived pre-machined. I’d have struggled to mill the spiral for sure.

(I’d probably have punted and taken it up to John’s placeand have him show me how it’s done!).

The Hemingway plans and castings are really nice, by the way.


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