By Kevin Ferguson
Chris Heapy described how he improved upon the woefully inadequate depth stop on his Naerok drill-mill in this article.
A fine idea, and worthy design but my machine, a Jet-16, differs somewhat from Mr. Heapy's:
The rod is secured by a 3/8"-16 nut threaded onto it's lower end, having passed through a plain (unthreaded) 3/8" hole in the cast collar encircling the quill. Here is a (poor) picture of the rod from my machine.
This rod passes up through a boss on the main head casting, which has been bored out to 5/8" and the top is spot faced, rather than being left as-cast. It is upon the spot faced surface that the depth adjustment nuts bear.
Enough of that, here is a discription of my changes:
A Couple of additional notes:
Since the castings on my machine had nice clean holes already, and no good way to bore them out sprang immediately to mind, I only scraped the paint from the holes. (the better for the JB-weld securing the bush to stick to)
To accommodate the existing 5/8" hole for the bushing, I reduced the stop rod diameter to 1/2".
To better accommodate the smaller stop rod, I reduced the main body of the clamp to 3/4". I kept the 5/8" diameter for the cotter housing.
I used 1" brass for the bush rather than gun metal (bronze?) simply because it was at hand. It seems to be working fine.
As Mr. Heapy warns it might, the upper hole in the head casting proved to be out of line (by approximately 1/16") with the rod mounting hole. I tried his suggestion for correcting this. (eccentric boring of the bushing) Those who are quick with arithmetic might have spotted a problem here. For those as slow as I am, here is a picture which will make things clear! ….If I had actually measured the eccentricity, I might have realized the problem before ruining the bushing. Measuring the eccentricity is a bit of a problem: I thought I was being ever so clever with the transfer punch! Instead, I bored the replacement bushing concentric, and did this->
To correct the misalignment, I turned the 3/8" mounting end of the stop rod eccentric. This left little or no shoulder on one side, so I added a 3/4" collar, silver soldered to the stop rod. After soldering, I faced a square shoulder on the lower end of the collar, and milled a pair of wrench flats. Here is a picture showing the collar. Though the eccentric end is hidden by the casting, note the spot face on the casting is eccentric to the rod. I had to do some filing & scraping on that spot face,in order to keep the rod from binding over the length of the quill travel. (the top of the casting was not square to the quill travel, causing the rod to tip and bind) You can see some of the filings, and the marking compound I used to indicate in which direction to vary the fit. A looser bushing would have eliminated the need for this, but I wanted a close fit to reduce rotational play in the quill, to improve upon the modification partially visable at the left side of the photo, and discribed below:
An earlier improvement to my machine was the fitting of a dial caliper to indicate quill travel. In order to keep the clamping handle clear the dial, I made the main body of the clamp nearly three inches tall. Here is a picture. It couldn't be much taller, as it must clear the belt gaurd when "parked". The rod was made longer as well, to allow parking room beyond full quill travel.
As the above picture showed, I didn't use a ball handle. The unit pictured was fabricated from 1/4 and 1/2" drill rod, with a brass knob a the end. One of these days I will make a ball turning device, and can then fit my projects out in fine english style. This handle is silver soldered to a 1/4"-20 shaft, rather than M6x1. I can see why Mr. Heapy used 6 mm, as 1/4" would seem to allow no clearance of the stop rod. However, in two tries (see below) the 1/2" reamer did not break into the threads. This may be because a standard 1/4" bolt is actually a few thousandths undersize, or perhaps the soldering clearance (punch pricks) allow it to work.
My first clamp failed at the solder joint. (photo) Apparently I didn't get one of the pieces adequately clean. It did not work so well anyway (the 3/8" cotter bore was a little rough) so I started fresh. I made a "D" bit to ream the replacement, rather than leaving the cotter bore as-drilled. With a smoother bore for the cotter, the new clamp works well, and the solder joint is holding so far. (knock wood!)
I can report that Mr. Heapy's idea of waiting to bore the cotter hole until the two clamp pieces have been joined worked out fine for me. Except that on the second clamp, I had used a 6-32 screw to hold the two pieces together for soldering. The solder did not bond to the screw, so I removed it before boring, figuring such a small cross hole would not interfere with the drilling & reaming. When my 1/4" pilot drill hit this hole, both the cutting edges grabbed, shattering the drill. This is why we wear safety glasses in the shop!
I mounted the rod on the lathe, and scribed a scale
directly on it. I set up a dial indicator to measure carriage travel (easer
to reset at end of travel, than if I had used the compound). I used a magnetic
pendulum type protractor on one of the chuck jaws to make 23 degree scribes
for 1/8", up to full circles for the inch marks.
These are a little hard to read. I may need to come up with an improvement down the road, but I think with a caliper mounted as I have, it is easy enough to read the depth on the first hole, and then just mark it with the stop for additional holes or boring passes. I like Mr. Heapy's idea of a collection of setting blocks, though I haven't yet made them.
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