Round dial apron oil pump, some observations

I'd like to know more about the apron oil pump, so I pulled mine this morning. I wanted to flush the apron again anyway, the clean up and reassembly I did earlier this year loosened some sediment that you could see in the new oil. Also I am not satisfied that the pump is working correctly and I wanted to reseat both check valves. So in the process, I made some observations that I don't think have been mentioned in previous threads about this pump.

First off, here is a picture of the pump and the cam that drives it. Calcs are shown on the paper, sorry fo the small photo size:



Here is the lever arm that drives it:



So if my calcs are right, each full stroke of the pump moves the lever arm 0.186", and the lever arm has a 2:1.5 ratio, so the piston moves .14". The diameter of the piston is .152", so the displaced volume is .003375 cu. in. or .055 cc. not a lot.

The next thing I was interested in knowing was if the wear on the lever arm (where it rubs against the cam) had been corrected. I brazed the worn area and added about .1" of silicon bronze filler. After using it a couple months I could see where it was rubbing, and all looked good, but the question was still how to check if it was correct. I think the designers of the pump added a feature that makes that check very easy. On the bottom of the pump there is a ¼" hole. If you place a drill bit in the hole, it stops the piston rod precisely at the point where the piston is entering the outlet hole for the pump. Here are some photos that show this:

¼" drill bit inserted in the alignment hole:


The piston stopped just inside the edge of the outlet hole:



Note that the outlet hole is .093" dia, so if the piston is exactly mid-stroke with the drill bit inserted, it would have .07" of stroke remaining, which would take it to the edge of the outlet bore... very precisely made, these little lube pumps.



The next step was to see where that spot occurred when the apron hand wheel was rotated. Continued in the next post.

With the pump mounted back in the apron, I used the drill rod to find out where the piston was in its stroke. The piston return spring held the drill rod in place except when the cam lobes were contacting the lever arm and the piston was retracted. It turns out that the points where the drill rod was released were about 180 degrees opposed, relative to the apron hand wheel. Here are some pictures that show the release points (look at the hand wheel knob positions). You can see the drill bit projecting down. When the hand wheel knob was in the bottom half of the rotation, the drill bit was released so the piston was in the intake portion of its travel. Each rotation of the hand wheel drove the piston through one cycle. A complete trip of the apron along the bed takes 21 or 22 revs of the hand wheel, so the pump should displace about 1cc.





So I think the pump geometry is close to being correct, the brazing corrected the wear.

I’m looking for the Bijur part numbers for the check valves used on the Round Dial apron lube pump. I’ve checked all the PM threads that show up with a search in the Monarch Forum for bijur check valve, and none of them have that information. There was one thread that had the part numbers for Square Dial check valves, but the outlet check valve is different (at least they look different). The inlet check valve is A3889, with gasket A3772. The outlet check valve for a square dial is B3905.

If I remember correctly I have seen numerous posts stating that Bijur parts are NOT that expensive when ordered from Monarch.

dinotom said:

If I remember correctly I have seen numerous posts stating that Bijur parts are NOT that expensive when ordered from Monarch.

Click to expand...

Terrie said that the check valves are not available for the round dial. The only option available from Monarch for a round dial is a complete oil pump, for $385. I asked her about the square dial check valves and she was not sure if they would work.

She quoted $15 for the square dial outlet check valve (in stock) and $110 for the inlet check valve (two week lead time). I ordered a square dial outlet check valve from Monarch, and will see if it works for a round dial pump, and I ordered an A3889 inlet check valve from Bijur ($19) along with a B3905 outlet check valve ($21) so that I can compare it to the one Monarch sold me. Bijur is out of stock on the A3889 and it has a 4-6 week lead time, so it will be a while until I get this issue resolved.

Terrie also told me that the A3889 and B3905 Bijur part numbers are not what Monarch purchases from Bijur.

If the parts don’t work on the 1940 lathe I will use them on the 59.

Dave
Great thread. Happy to see you did this study.

Question: did you get the bijur items # A3889 and B3905 and did they work on your 1940 round dial. I have a 1939 10ee and want to rebuild the pump

Thanks

Jim Murphy

It's interesting to see the full stroke volume calculations. Thanks.

If I understand this correctly the cam on the apron hand-wheel shaft draws the pump ram back and charges the pump with oil.
The spring forces the oil out which is then metered by the valves in the apron and saddle.
Consequently the full stroke volume may not be delivered before the pump is re-charged, especially if the carriage is racked quickly along the bed.

Probably an academic question but would be possible to calculate how long it would take for the pump to deliver it's full stroke volume from the sum of the metering valve feed rates?
ie with the pump fully charged but the carriage static.