Visual or dimensional difference......
- Thread starter Robert E Naess
- Start date
Thanks Roger, basically what I was thinking, probably back in the middle ages (the age when Vins weren't worth making top quality spares for) you could mix and match, but no need now.
I'll stick to my 2 start pump (worm and plunger) with a free flow paper filter and no metering wires, the more oil I get to loaded parts, the more I like it. I've even contemplated putting a restrictor valve in the return after the head, to build a bit of pressure, but I think that's one step beyond.
H
I'll stick to my 2 start pump (worm and plunger) with a free flow paper filter and no metering wires, the more oil I get to loaded parts, the more I like it. I've even contemplated putting a restrictor valve in the return after the head, to build a bit of pressure, but I think that's one step beyond.
H
Gentlemen, I would invite you to perform a small thought experiment. Imagine that you have a two start worm and that you use a white marker to trace along the top of one of the threads. What would you see? A white line with a much coarser pitch than that of a single start worm and with another thread unmarked weaving its way equally spaced between the marked thread. Now if you can imagine that, try also imagining what would happen if you tried to force a bolt with half the pitch into a nut with double that pitch. Would you keep forcing it in or would common sense prevail and would you give up before you destroyed something That is the situation of using a twin start worm with a standard single start plunger. The fact that it is not clear to a casual visual inspection that a two start worm has a much coarser pitch than a single one does not mean that it would be good practice to use a mismatched pair. You can get away with it for a short time on our worm and, very small, worm wheel combinations (i.e. the small diameter plunger) but it is going to wear out quickly.
Hi TT
I understand the logic and your concerns. But if we compare the two plungers we can see the tooth pitches are identical. And if we match the two worm types together, tooth to tooth, the spacing should also match one to another.
Machining/ turning the teeth of a single start worm is the same as turning a thread on a lathe except for the tooth profile that is. And is similar for the two start worm except that we cut two threads, each with twice the pitch of the single start worm and where the second ‘thread’is staggered by an amount, (the Lead) that is equal to half the pitch. So we cut one thread, then move the lathe’s toolpost by an amount equal to half the pitch, and cut the second thread.
May be a better illustration/explanation would be two springs with coils spaced .25” apart meshed with each other giving a pitch spacing of .125”.
To manufacture a two start worm is not difficult. Unfortunately the same can’t be said of a matching plunger with angled teeth because the angle is not ‘straight’ its a spiral.
Hope that helps
Regards
Roger
Ps Thanks Moderator, for adjusting a previous post of mine
Hi TT, I don't think the nut and bolt analogy works in this case. If you draw your white line with a pencil, the pencil won't stop the bolt turning whether the bolt is 1, 2 or 20 starts, but as you say, if you put a 2 start nut on a single start bolt it will jam. Provided the pitch of each start of the twin start is twice the single start pitch, all worm teeth will engage valleys in the plunger. If there's enough (too much) backlash the system won't lock up.
I'm not saying it's right, and I personally would never do it, but it's possible people are unknowingly using a 2 start worm with a single start plunger.
H
I'm not saying it's right, and I personally would never do it, but it's possible people are unknowingly using a 2 start worm with a single start plunger.
H
Trev did a bit on another thread, Where he grinds a ring around the plunger, For long life, But I didn't understand how it would work, Cheers bill.
If I have understood it correctly Clevtrev's modification is a groove around the plunger where the run out of the teeth are. This means that any tendency of the worm to bind up on that run out will not occur. Clevtrev will no doubt correct that if I have it wrong. Going back to my attempt to explain the twin start problem; imagine removing one of the threads on a two start worm and then offering it up to a single start type plunger. Think of the angle of contact between that single tooth on the worm and the teeth on the plunger.
I remember Syd posting that the factory used two-start pump worms on standard pumps. So how??????
A remote controlled drone aircraft engine would not have to last long. Although the engine proved more reliable that the early remote system......what were they thinking....???