Tail Shaft Mod

This is a modification and fix for the tail shaft. It is really three thing that were done to make it better. The combination of these fixes/mods did wonders for its smoothness and operation.

First was the screw itself. I noticed a hole in the end of it at one time and thought maybe there should be some kind of pillow block pressed into it but the exploded drawing didn't show any thing so I assumed it was a hole for turning it on center for creating the threads on it. Then it struck me that if I built a little Delrin pill that pressed into it I could extend the release point of the tapers a bit. Here is what I came up with.

Here it is pressed in.

The hole in the end of the screw is Ø.1220 and about .2188 deep. I figured that if I gave a little flat of about .100 thick that would extend the ejection distance that much which makes the Dial Stop a little more comfortable when ejecting a tool. I also knew that it would have to clear the hole in the shaft where it screws in, so I came up with a Ø.336 for the pillow...and off I went.

I chucked up a piece of 3/8" Delrin and proceeded to whittle out what I needed. I messed up and undercut the press in part the first time, so I parted it off and started again being very careful to walk up on it slowly until I got the tight press fit I wanted. The Spring Back properties of Delrin

really work for this kind of application as I knew from my Carb Tool and the spline broaching I did for that. My pressed in pin part came out to be ~Ø.1305-.1310 (a little taper to it) and .20 long after clean up and press test. The pillow final size was Ø.3345 x .128 (instead of .10). It all took about 25 minutes to figure out and make and it works great!

The second fix/mod was something that had been bugging me for a while. The milled slot for aligning and setting tension on the shaft was cut with a rock and chisel, I'm pretty sure! It was always rough and difficult to set the dog point set screw to get a smooth slide and no side tilt. It would tilt sometimes about 5° if I didn't have the top lock snugged up a bit when I started an end mill.

Soooo, this was a 2 part fix, starting with the milled slot in the shaft. Unfortunately I didn't take before pictures but you can see remnants in the corners I couldn't clean up.

I used an rubberized abrasive wheel on the Dremel and used a small piece of .125 AL sheet with that I rounded to match the end diameters, then wrapped emery around it to work the ends by hand.

It's a heck of a lot cleaner than it was but not perfect. I ordered a set of rubber polishing wheels of different shapes, grits and sizes for $15 on Amazon (now $25) which should be here tomorrow and will try to get this a little cleaner. In the following pictures you can see some of the issues with the sides of the channel.

The next issues was the dog point set screw. My dog point itself was a metric 6mm x 1.0 x 16mm but when I mic'd the dog point it was 3.75mm not 4.0 which is spec. The slot mics out at 4.03-4.05 mm (.1590-.1595) so it was pretty close to what it should be considering the rock and chisel. The screw was also cobby on the flat so I thought I would make a new one out of brass. Also note the manual and exploded drawing calls for a M5 x 16mm?

Here is what I came up with.

It measures out right at .7 long with the threaded section being .344 long and the dog point is Ø4.02mm (.1585) and right at .08 long. I also double nutted a screw and chucked it up to face off about half the thickness of the original nut (like a thin/jam nut).

Then made the pretty knurl part using my spread sheet, because this was a piece of that old crusty ground rod I had. My initial OD for the knurling, after clean up was Ø.3665 and the spread sheet calls for a Ø.3624 for a medium knurl. I hit Ø.363 and put the knurl tool on and this is what I got...one of my better knurls. Note: after knurling the OD is right at Ø.380...so that might give a clue to tooth depth, eh?

It's a good size for the fingers and still get a wrench in to cinch it up. The best part is the fit in the milled slot as you can see below it stands on its own and slides Real Nice on the polished surface.

Note: in the above you can see the faint 1/16" markings...and why I built the Dial Gauge system for it. If I were building barns it would have been fine...And shined a light on it just right! 8-))

In these pictures you can get a clue about how cobby the channel is on the sides...the bottom was even worse. Once I get my new polishing tools I will clean this up even more.

Overall with a little White Lithium grease the shaft fix, new set screw, and screw tip make the shaft assembly Much Better than it was. It's easier to adjust and the handle cranks very smoothly now and most of all it doesn't rock over any more when doing end mill operations.

Another great mod/fix for the Mini that makes me happy and easier to use...what more could I ask for! OK, then...I am Still thinking about a linear scale instead of the dial gauge.... @¿@

Epilogue

I received the polishing wheel set and used them to finish up the slot. I want to give a little review of these since I put the link up for them and saw they raised the price, since my posting. The set is pretty good over all but found that the rubber in them is pretty low grade and gets consumed quickly. The different grits are nice but could barely tell the difference between the 240 and 600. The cylindrical ones are about 1/4" diameter so I needed to turn off a bit with a piece of sheet metal (edgewise) to fit the slot the way I wanted to polish it. The conical ones fit in the radius well but did get consumed quickly. The circular wheels have a nice sharp edge to them so was able to get the corners in the run of the slot much better. The wheels are pretty good for the money over all but for the new price I will use them a little more judiciously.