The Shop => Tools => Topic started by: vtsteam on April 28, 2022, 08:48:39 PM

Title: My Round Column Mill Drill
Post by: vtsteam on April 28, 2022, 08:48:39 PM
I'm going to continue with some of the project work I've been doing on my Enco mill drill here, since it doesn't quite fit the Electronics section where I was talking about my DIY bluetooth DRO project.

One of the mill's problems, is that there is a lot of radial play in the quill. Investigating, it turns out that there is a guide slot and a threaded guide pin and stop nut on the left side of the mill, as you face it. The fit seemed poor. and that allows a lot of play.

Well today, I decided to check both the threaded pin and the slot to see whether I could fabricate a better fitting replacement. Turns out the pin end is 7mm in diameter, and the slot is 8mm. It looked like neither was worn, so that was the actual factory fit!

I checked the threads quickly with my calipers -- a little under 10mm diameter , so probably a 10mm screw (with a turned 7mm tip). So off to town -- 30 mins of driving, there and back -- to buy a single 10 mm bolt. I don't have a 10mm threading die, or a 127 tooth gear for the Craftsman lathe. So a bolt it is. We're still heavily into inches here at most hardware stores;  metric fasteners are specials, and cost more. I don't keep much on-hand, and I didn't have a 10.

Just before I headed out the door, on a whim, I picked up the narrow stop nut and tried it against a 3/8" piece of all-thread leaning nearby. Well, it screwed on easily!  :scratch:

What the? Why would they put inch fasteners in a Taiwanese mill drill? Didn't make sense. But coincidentally I had just seen a "Winky's Workshop" video where Winky himself stated that the cover plate holding his similar mill's crank handle was also an inch size -- quarter inch bolts! So well, I believed this must be more of the same thing.

What the heck, that's easy, I had plenty of 3/8" - 16 bolts, but I needed to mail some letters for my wife in town, having volunteered earlier -- thinking to make getting a single bolt run seem more reasonable. So I decided to go as promised, maybe I'd find an unusual longish 3/8" setscrew in town, which would be easier to hold in the lathe when turning the tip down to 8mm. No head to deal with.  :dremel:

I got to town, and after finding an allen head machine screw of the right size and length, I brought it to the counter. And then found that I'd forgotten my wallet!  :bang:

Well, not to be done in by a damn bolt, I asked the lady clerk to hold onto it for me, ran back out to the parking lot, and scraped enough quarters out of the car glove compartment ...and back seat... to buy it. Which was admittedly, pretty pricey at a buck forty-nine, but, by golly, that bolt was the whole purpose of this mission, and I wasn't going home empty-handed! Well, besides mailing those letters at the post office.  :thumbup:

Driving back home I was still thinking about why that mill had inch fasteners. Or how many it had. Were they mixed? Why would they do that? Not complaining, it's actually convenient, but you know, surprising! I looked forward to getting that damn play out of the quill so I could move forward with my Z axis DRO scale mount. Something very satisfying about improving a tool by removing play that has bothered you for, well years.

Well you've probably already guessed where this story is going... downhill..... The bolt wasn't right. I mean it seemed to be right for about 5 or 6 threads deep. It screwed right in, maybe a little too loose at first, but getting tighter as it went. But uhhhhh, then it stopped.....

Hmmm. Why is that? Is it hitting the column slot? Nope doesn't seem to be...... :scratch: :scratch:

Uhhhhhh, maybe it really is 10 mm........ Is that possible? Are they that similar?  :scratch: :scratch: :scratch:

Well, you learn something new every day. Or maybe something old. Or maybe you never learn.....  :wack:

And that's what I accomplished today on my mill drill.
Title: Re: My Round Column Mill Drill
Post by: awemawson on April 29, 2022, 02:40:15 AM
I do have a vague recollection that when Taiwan was being heavily supported by the US back in the mid 1960ís to develop an industrial base they set up a Design Bureaux to produce machine tool designs that were freely available to any local firm wanting to produce such things. This resulted in many machines being to all intents identical even though made by different companies. However some companies inevitably made changes particularly if they were already tooled up in (say) metric fasteners despite the design calling for Imperial. So you find metric threads on bolts with Imperial hex heads and vice versa.

What didnít develop at quite the same rate was the concept of standards and testing. Much the same happened in Japan after the war where quality was atrocious until they developed extensive quality standards and enforced them. BS5750 which translated later into the ISO9000 series of standards was based closely on this early work in Japan.

 . . .  But where this leaves your screw thread Iím not sure Steve !
Title: Re: My Round Column Mill Drill
Post by: RussellT on April 29, 2022, 05:46:10 AM
Uhhhhhh, maybe it really is 10 mm........ Is that possible? Are they that similar?  :scratch: :scratch: :scratch:
Hi Steve

I have come across this before on a car I own. The engine and gearbox are different ages, the bolts into the gearbox are 10mm and the bolts into the the engine are 3/8.  It is possible to put the 3/8 bolts in the wrong (10mm) holes but not generally the other way around. :loco:

Worse - I also found 3/8 threaded brake pipes threaded into 10mm threaded brake calipers. :bang:

However this doesn't help because if it's a 10mm hole or a 3/8 hole I'd expect the 3/8 bolt to fit. :scratch:

Title: Re: My Round Column Mill Drill
Post by: vtsteam on April 29, 2022, 08:36:30 AM
Thanks guys, I see another trip to town in my near future! I think buying a 10mm die and tap would probably be smarter than just a 10mm bolt. After all, steel of all sorts is plentiful here, and a bolt would require modification anyway for this particular function.

Even more radical (read sensible) would be completing my lathe electronic leadscrew project, since that is functionally tested, mounted in a nicely painted aesthetically matching housing, the stepper and tach mounted to the lathe already, and basically just requires putting the power supplies and wiring in place in a separate box. It should do any of the pre-programmed pitches at the flip of a few switches.

Hey, it also does this amazing thing, too, called power feed. I'll have to experience that some time. Of course the downside is that the knobs on my handwheels will start to lose their present amazing shine.

Andrew, I worked in a quality systems software house once upon a time in Boston doing ISO 900x software troubleshooting support and datatbase documentation. The system ran under Lotus notes with 32 separate databases, all integrated together. Customers were 3M, Kodak, Chrysler, Cummins, Motorola, etc.

Okay, back to this unknown size screw hole in my mill......
Title: Re: My Round Column Mill Drill
Post by: vtsteam on April 29, 2022, 09:53:16 AM
10mm it is.

Picked up bolt, tap and die for 10mm, and 8mm, too, for good measure. I already have a 6 and under set.

On with the show....
Title: Re: My Round Column Mill Drill
Post by: vtsteam on April 29, 2022, 02:22:56 PM
The bolt was a little short, so I decided to turn down the head rather than saw it off to  make the quill slide screw.

To hold it by the threaded end in the 4-jaw, I decided to make a split bushing. I found a piece of cold rolled round stock, faced and center drilled it. The 10mm bolt measured .384" actual over the threads. The closest drill I had that was a 25/64", which is .390, so I drilled the piece through, then slit it cross ways into four fingers almost to the end with a hacksaw. In one cut, I slit it all the way to the end.

This gripped the bolt threads well in the 4 jaw. I indicated the bolt body in, and started turning the head off with a carbide insert -- the same one I'd used for iron castings. Seemed to do well -- the bolt was an 8.8 grade.
Title: Re: My Round Column Mill Drill
Post by: vtsteam on April 29, 2022, 06:55:12 PM
The split bushing was also handy for holding the screw in the vise while adding a screwdriver slot with a hacksaw.
Title: Re: My Round Column Mill Drill
Post by: vtsteam on April 29, 2022, 07:02:46 PM
Finally the quill screw was finished. Here are both new and old together. The new screw guide pin is .030" (0.76 millimeter) larger than the old one. Makes a very big difference in radial play for the quill!
Title: Re: My Round Column Mill Drill
Post by: vtsteam on April 30, 2022, 12:49:11 PM
Yesterday, after solving the quill play problem I went on to build a Z axis DRO scale mount. (This is a continuation of the DIY Bluetooth DRO project started here:,13501.0.html ).

Here is the mount, fabricated out of 2" x 2" x 1/8" angle iron and some 3/8" flat bar. The angle iron serves as the moving scale mount, and also as a guard for the scale.
Title: Re: My Round Column Mill Drill
Post by: vtsteam on April 30, 2022, 01:02:13 PM
The Z axis scale mount bracket simply clamps to the lower quill casting. The angle iron is angled in relation to the clamp -- not so visible here. It was positioned before welding on the clamp bracket so that it was square to the side of the mill head, and ran true to that surface when brought up and down to the limits of quill movement.

(BTW, all of that thick factory filler slathered onto the castings has cracked and flaked over time, as can be seen here. At some point this summer I'm hoping to refinish the mill. I do wonder about what it is, because it's reddish in color underneath the paint and whether it's just Bondo-like polyester filler, or actual red lead -- which would be highly problematic.)
Title: Re: My Round Column Mill Drill
Post by: vtsteam on April 30, 2022, 05:03:40 PM
Finally I made a small bracket to support the Z axis read head and drilled and tapped for it into the mill head. The location was clear and about 3/8" thick iron, with access behind, so I felt fairly confident about poking holes.

Adjustments to prevent any binding in the slide were easy to accomplish by just keeping the end screws loose in their slots on the scale brackets, and traversing the quill to an end stop and tightening them alternately.

A calibration test as had been done for the X and Y Axes yielded a CPI of 2562.5, half way between the other two. With that, a 3 inch traverse was right on the money, and repeatable to zero and back several times. I like this particular installation as it retains the stock Z axis stop, features a stationary head (and therefore wiring), and is very easily removable. Actually, the same is true of all three axes. I lost no features, have the same travel ranges as before, all heads are stationary, and all can be removed with 4 screws or less.

I only have to make a guard for the X axis scale, neaten the wiring, and possibly add a display (phone or tablet) holder and the DRO installation is done!  :ddb: