The reconditioning of the pump latch for my Monotype caster is now complete. I found some donors for the missing screws in my parts stock. There were two of the actual latch trigger assemblies there (but not the rest of the latch) so I took two screws from one of these.

I used the Loctite Form-A-Thread kit to improve the fit of these screws in the holes I had tapped for them. The tap I had used was a standard modern #8-36 which makes the threads slightly larger in diameter that these screws, and perhaps the vee angle of the threads is different as well. The Form-A-Thread kit consists of a 2-part epoxy filler material and a coating to apply to the screws to prevent the filler from sticking to them. You coat the screws, measure out equal amounts of the two components of the epoxy, mix well, put it in the holes, and screw the screws into place. After 5 to 10 minutes you remove the screws again and give the filler half an hour to finish curing. This stuff is usually used on larger holes and I found I had a bit of trouble getting any down into these relatively small holes, but I seem to have put in enough that the screws now thread in without any slop. I was thrown a bit by their statement that the filler starts to gel in about 5 minutes, but I was finding that the remnants on my mixing board seemed to remain liquid. Perhaps exposure to the air slows or inhibits hardening.

In any case, everything is painted and assembled now, and a few drops of oil makes everything operate smoothly:

The long spring along the back should probably be replaced. It already had an end broken, and when I tried re-shaping the last turn of the spring to make a proper hook again, part of the wire snapped off so perhaps the entire spring is suffering somewhat from metal fatigue. Fortunately, I already have some #24 steel music wire to make a replacement when the time comes, and I have also already measured this spring so I have all I need to replace it. Someday…

So the only task left is to make the longer spring rod. Oh yes, there is also the extended-stroke piston rod to complete.

The new spring rod might be a simple part to make, except that one can’t turn a 24″-long part on a 7×20″ lathe.

I thought the new spring rod I have to make for my Monotype pump would be relatively easy to do, after all, it is just a length of 5/8″ round rod threaded at both ends. The problem is that my Myford ML7 lathe bed is too short to hold the part, and the spindle bore is too small to allow the rod to pass through.

So now I have to come up with another way to do it. One way is to find someone with a larger lathe who will let me use it. Another possibility is to use the CNC capabilities of my mill to shape the ends of the rod. I will have to ponder the possibilities for a few days.

In the meantime I now have a Loctite Form-A-Thread kit for repairing stripped threads, and I will see if I can use it to improve the tapped holes in the pump latch.

The pump head on my Monotype Composition caster is now back together, except for the pump springs and related parts, which I have to replace with home-made ones to accommodate the pump latch mechanism.

The parts to be made or modified are quite simple, so this is the “drawing” I am working from:

This is the drawing, such as it is, that I am working from. It shows (top) an extended-length pump spring rod c20H1, (left) the existing lower spring abutment a20H12, (right) the socket in the upper crosshead a19H3, (bottom) modifications to my home-made a19H5, and (lower right) dimensions for a new piston rod sleeve b20H7.

As it turns out, the thread pitch on the upper end of the spring rod is 11TPI not 12 as shown on the drawing. Modifying the crosshead stud a19H5 was the easiest and done first: I just had to run the appropriate threading die another inch up the rod.

The piston rod sleeve was the next to make. Starting with a length of 1″ diameter hot-rolled round stock (I did not have any cold-rolled), I faced one end, drilled a ¾” hole down the center, and bored partway in to match the diameter of the step in the lower spring abutment.

This shows the sleeve with one end bored out. The boring tool is a bit out of focus. This diameter actually only has to be bored a little over 1/16″ but I gave it extra depth because it looks better.

I then reversed the sleeve in the lathe, bored the other end (so it could be installed either way up) and faced it to the correct length. Because I used hot-rolled stock, the outside diameter was covered with mill scale which I removed by filing it off, although there is a bit of scale still showing in some pock marks. I would not have had to do this had I started with cold-rolled stock. All the sharp edges and burrs were removed, giving the finished part, which is a nice snug fit with the spring abutment.

The last part, the longer spring rod, is another story and another post…

After determining that I had a way to drill the necessary holes without any new tooling, the repair of the threaded holes on the Latch Abutment (58H1) is finished.

Even with the holes properly center-punched, I had a little trouble with the drill drifting out of position on the right-hand hole but I managed to get the hole back to the correct position with only a shallow out-of-round spot. A close look at the photo will show the out-of-round hole. You can also faintly see the circle of brazing that holds the repair plugs in place.

Tapping the holes turned out to need no special tool: the body of my tap wrench was small enough and I just had to put up with the tediousness of sliding the T-handle across every half-turn.

Now I just have to paint all the parts and re-assemble the latch. I have spares of the small screws for the repaired holes. They are original parts, and although they are not an exact match for the tap I used (both the diameter and thread angle differ a bit) their heads have the shape to fit the countersink in the actual latch plate. I don’t feel like taking a pair of modern #8-36 screws and having to re-shape their heads only to have two screws that won’t fit anywhere else on the machine. Another option would be to use a product like Loctite Form-A-Thread to fill the thread in the holes to their proper dimensions.

My use of a photo editor to measure the hue and saturation of the paint colours paid off. I had inferred that I had to add to my new paint a mix of two parts red and one part blue. The correction hue at full saturation was a reddish magenta, but the mixed paint I added was a dark reddish brown. I think the resulting gray is about as close as I can get when trying to match gloss and semi-gloss paint.

This shows samples under room lighting. Lower right is the good match, upper right is the previous match, and the small part in between is the colour reference I am using.

These are the same parts illuminated with the camera flash. The part in the upper right is much more obviously too blue-green.

My suspicion is that the original paint is a mix of litharge (basic lead carbonate, aka white lead) and carbon black, both of which are somewhat warmer tones that the modern gray paint which is more likely titanium dioxide and possibly iron oxide black.

In my projects to refurbish my Monotype pump and install a latch mechanism, I am now at the stage of needing to repaint some parts, and I am finding it to be a tricky job.

For one thing, In can’t rely on the colour on other parts of my caster because they aren’t clean enough to use as a standard. The dirt on them is sufficiently tenacious that any attempt to clean them would also remove some of the paint.

As a result I instead have to use some new (or like-new) parts from my parts stock, and in doing so I am finding that Monotype did not seem to be consistent in its colour choice. I selected one (unidentified) part which seemed to be the correct colour to match the rest of my caster, and I’m now trying to get a matching paint.

I only need a half-pint of paint, and paint stores are generally unable to tint such small quantities. Furthermore, this is a rust-preventing metal paint, for which tinting choices are limited.

I have started with gray paint as a base, and I felt that the actual paint colour was bluer and darker than the paint I had, so (in a small cup) I mixed up several shades with a bit of blue and/or black added. I thought I was close (and it was getting late) so I painted all but one of the parts. Upon finishing I looked at them and felt they were way too blue, so I will have to try again on a second coat.

I took photos of some of the colours I had mixed alongside the reference part, and the colour-picker in the photo editor is telling me that the target colour is lighter and oranger than my original gray, just the opposite of what I thought! I tried to take the photo in a manner to avoid the specular reflection from the gloss paint, but the gloss reflection may still be messing up my measurements.

Various colour paint samples are on the left, and the reference part are on the right.

This is the same photo blurred to allow reasonable measurement of the colours in the photo editor.