# PMR model machine tools and some jigs to build them



## mklotz (Feb 20, 2008)

Over the years I've finished all of PMR's machine tool models. My wife keeps bugging me to build the dollhouse scale (1:12) shop to contain them and operate them with scale overhead line shafting. I never seem to get around to it. (Besides, if I build it, I won't have any place to store it.)

Nevertheless, to demonstrate to kids how machines were powered before the ubiquitous electric motor, I built a small demonstrator using an old circuit board test jig as the skeleton.







The (adjustable) overhead shaft hangers are available as kits from PMR and they work very well.






The milling machine model uses two 3/16" brass balls as part of the sliding universal joint that transmits power to the table leadscrew. These balls have to be drilled with two orthogonal 1/16" holes to accept the yokes that make up the universal joints.






To accomplish this, I made up the little jig shown below. A chunk of 1/2" steel is drilled and threaded to accept a matching 3/8" lock screw that has a centerdrilled hole in the end. This conical depression, along with the other cone formed by the tap drill used to thread the chunk will serve to center and clamp the brass ball when it's inserted in the jig. 






Here the ball is shown mounted and clamped by the lock screw. At this point, the chunk is stuck in a collet in the lathe and a 1/16" drill passes through the hole in the front of the chunk, through the ball and into the centerdrilled cavity in the lock screw.

Prior to mounting the lock screw, I measured from the face of the chunk to the back of the ball with my mike. After the first hole is drilled in the lathe, the chunk is transferred to the mill and, using that dimension, I can locate the center of the ball and drill the second hole secure in the knowledge that it will be perpendicular to the first.






When I built the demonstrator, I quickly discovered that miniature belting doesn't work like full size. Full size belts have enough weight to them that they will "hang" on the pulleys and grab well enough to transmit power even if they aren't absolutely tight. The miniature belts are much lighter and need to be snugged up carefully or they'll slip.

Rather than shim the models in order to tighten the belts once glued, I built this jig to allow me to mount the belts, tension them in place, and then glue the ends.

It consists of two tiny carriages with male dovetails on the bottom which ride in a matching dovetail in the base. Two brass strap clamps secure the two ends of the belts to the carriages. A long screw passes through one carriage and is threaded into the other such that, when the screw is tightened the two carriages are pulled together thus tensioning the belt. Once properly tensioned, a couple drops of super glue and a tiny clamp (not shown) secure the two belt ends.


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## BobWarfield (Feb 20, 2008)

I love these little jigs!

I was just looking at those BB's and thinking, "Dang, that had to be a b***h to drill!" But no, with the right jig tool or gadget, you can do almost anything.

Marv, sometime you should line up all the tooling you've made that's small, say anything less than 4-6" square. Put it all on a table and shoot a photo fo the lot. I'll bet it's an incredible array.

Cheers,

BW


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## tattoomike68 (Feb 20, 2008)

Nice toys, how about a video of them running?


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## ChooChooMike (Feb 20, 2008)

Now Marv/steam engine builder extraordinare  .... let's talk about authenticity here 

You're supposed to be running the line shaft models off of probably a mill steam engine model like was done in the day. With steam, no cheating using air here ....  ;D

Great looking models BTW !! and VERY COOL little ball drilling jig !!


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## mklotz (Feb 21, 2008)

Bob,

It's my contention that, after learning the basics of operating the lathe and mill, model engineering consists primarily of learning to design jigs and fixtures. There are so many tiny, intricate parts and conventional fabrication techniques seldom scale down usefully so one is forced to think outside the box in order to get the job done.

If I see that the required jig/fixture has potential future uses, I'll spend some time designing and making it and add it to my arsenal. That was the case for these two since many features are replicated among the PMR machine tool models. Other j/fs are one shots and get recycled so they're not available for display.

Tatoomike,

I don't own a video camera so I'll have to wait for a show and corner someone with one to make an uploadable video.

Mike,

Yeah, I figured someone would make that comment. This was only a test piece to work out the bugs in running the machines off line shafts so I used what was to hand - a geared-down electric motor. While I already have the rope drive steam engine built to power things when the miniature workshop gets built,






the electric demonstrator remains very convenient for showing folks how line shafts worked without the need to drag out the compressor. Although, now that I have the airbrush compressor, that argument is less credible.


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## S_J_H (Feb 21, 2008)

Marv, very nice ideas! I am building the little engine lathe right now. It's quite a neat little model. This is my first time working with castings and these are probably the smallest parts I have worked with as well.
I am finding it a nice challenge. One thing I quickly realized is how much tooling I needed for this model. I had very little in the way of miniature cutters, taps and dies. 

Steve


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## mklotz (Feb 21, 2008)

Steve,

Feel free to contact me if you have any questions. My email addy is in my profile.

I think you'll have fun building the model. I certainly did. (Well, putting that chip breaker in the 1/16" square tool bit was a bit tedious but, otherwise, lots of fun.)


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## Bernd (Feb 21, 2008)

Nice job Marv. I like the jig for drilling the balls. Now I know how I can make a drive shaft for some of those "O" scale model railroad engines I want to build.

Bernd


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## BobWarfield (Feb 21, 2008)

mklotz  said:
			
		

> Bob,
> 
> It's my contention that, after learning the basics of operating the lathe and mill, model engineering consists primarily of learning to design jigs and fixtures. There are so many tiny, intricate parts and conventional fabrication techniques seldom scale down usefully so one is forced to think outside the box in order to get the job done.



Marv I think that's one of the best and smartest quotes I've heard in a long time. I would modify it to say "machining" rather than "model engineering." I would also add that I think metrology is the 4th leg of the stool after turning and milling. If you can't measure it accurately, you can't machine accurately. While I haven't built too many jigs yet, I have put my money where my mouth is. I have really gone out of my way to understand workholding on the lathe and mill, and I bought Carr Lane's book on fixturing, which was recommended to me on PM. It has been an excellent help. Lastly, I have worked hard at improving my measurement skills.

Best,

BW


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## Mcgyver (Feb 21, 2008)

Marv, very nice work, i really like that shaper and mill


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## mklotz (Feb 22, 2008)

Here are some better pictures of the shaper and milling machine











and the drillpress


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## ChooChooMike (Feb 22, 2008)

Thanks for the pix Marv ! I've got the kit for the drill press and thought I had the mill, but vaguely remember losing that bid on eBay.


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