Herewith I don't agree due to very bad experience with the setting of twin speed worm and new single plunger fitted . it lasted 10 seconds.
Regards, van Drenth JC
Visual or dimensional difference......
- Thread starter Robert E Naess
- Start date
Herewith I don't agree due to very bad experience with the setting of twin speed worm and new single plunger fitted . it lasted 10 seconds.
Regards, van Drenth JC
One thing I do think is worth checking, Put the plunger in the cases with the location screw in tight, I have found a few bind up when turned, I have ground a bit off the screw end or try another screw, Cheers Bill.
Bill perhaps that is a symptom of what Trevor was on about regarding the rearward end of the plunger teeth bottoming out on the worm. When I checked this on the race engine...I set up the plunger so it was in it's forward most position this with the location screw in position. I then removed the screw and pushed the plunger further up the bore to make sure this issue would not happen. Obviously on some plungers the teeth are different, but I think this is what Trevor was talking about...........Greg.
Hi TT, my original mischievous post that I thought might stir some discussion (the Forum seems to have been a bit quiet on these lately) mentioned the line contact. Worm gears aren't like other gears because the point (or line) of contact travels across the face of the mating gear, not up or down it. Provided the back of the tooth has plenty of clearance and the pitch of the worm between adjacent teeth is correct, the wheel/plunger will turn - not necessarily efficiently or with any longevity. Each start of the worm engages alternate teeth on the plunger, effectively making the plunger 2 start as well.
Just an extra point to throw into the mix - because of the rubbing action, most industrial worm gearboxes have a hardened and ground steel worm and a bronze wheel - I wonder if we should try a bronze plunger???
H
Just an extra point to throw into the mix - because of the rubbing action, most industrial worm gearboxes have a hardened and ground steel worm and a bronze wheel - I wonder if we should try a bronze plunger???
H
I know what you mean Greg , But I have found the groove in the plunger is not square, And the tightness not found untill all tightened up. Cheers bill.
Hello Howard and others, I am no engineer but as an astronomer my experience of worm and worm wheel drives is that for many telescopes from amateur sizes (mirrors or lenses 4"/100mm upwards) right up to telescopes in the 100"/ 2.5m range then worm and worm wheel drives were the norm for decades. These drives have to be ultra accurate with periodic errors less than one second of arc. At the bottom end of the range I have seen bits of studding spring loaded up against straight cut gears by one American manufacturer who should be ashamed of themselves. For the larger telescopes the worm wheel is typically one metre to two metres diameter and the worm 3 - 6 inches, 75 - 150 mm diameter. Reduction ratios are typically about 360 :1 and both larger and smaller are used. (And for those who have never thought about it a single start worm counts as one tooth so a single start worm in conjunction with a worm wheel with 360 teeth gives a 360 : 1 reduction.) However for this kind of accuracy the worms are not 'cylindrical', parallel or however one likes to think about it, instead they have a concave profile so that the worm mates with several teeth on the worm wheel at the same time and the pitch varies along its length. Machining such a worm is not for the faint hearted. As Howard wrote all the large drives of this sort which I have seen have bronze worm wheels and steel worms but they work at very low revs. Multi start worms and their mating bits were a regular feature of the distributor and/or oil pump drives on car engines for years. I think that Greg is correct above in that the life expectancy of a Picador engine was hours, not decades. Certainly people have got away with a mismatch of components on Vincents but how many hours they ran one never knows. I certainly do not want to 'preach' to people about this but why, once the problems have been made clear, would one want to use the wrong combination?
I see why you are concerned about jamming. My worm gear background is industrial drives built for an input speed up to 3000 rpm with a design life of 100,000 hours, accuracy is not a make or break requirement. Typical max ratio would be 100:1, but for a double worm combination that rises to 10,000:1, just don't ask about the efficiency, and I'm fairly sure if you used one of my type of drives, you'd be hard pressed to line up your telescope on a football stadium a mile away, let alone a star several light years away..
H
H
Pushing the plunger further up the bore would prove nothing, because the plunger simply run along the worm groove. The part of the assembly that touches first, is the extreme corner point of the worm tooth, that`s from the very first revolution. This removes the corner hardness so that now you get lots of friction between the contact points, and it just gets worse.
Ref. Mr Drenth. There`s no way the thing would wear out as quickly as you mention, somewhere in your assembly you have caused it to hang up.
Hello Trev, Does your groove go off at an angle ? Can't see for sure, If I did it with a grind stone, Would it mess up the hardness, Cheers bill.
No, it`s just a ring around. The main point is to make sure you start the groove just before the change in section of the tooth at the run out. You can see from that picture exactly how much contact there is between the tooth and plunger. that one had done a thousand miles.