MLoew (anecdotal)
I am sure glad you have two guides on the scotch yoke. I have some test papers where my father drew the yoke with only one guide. The note returned with the drawing cautioned him about having two guides (best) or one longer one, not more than 2d of the shaft. He lossed 20 points on the drawing. He was also advised to study the chapter on the yoke and always consider all the inputs on design.
circa. 1925
Maybe the solution is changing the basic concept, why not use an hidraulic piston, you can make it fit inside the 3" diameter tube, you can make it 5' long with no problem and you can adjust speed easily, power will be higher than any mechanical device you can use and you can also use neumatic power if your power need is low, the motor will allways turn the same direction driving the pump/compressor and the only drawback is the whole mess of controls, hoses and devices requiered, but it could be an alternative.
Can you use something like a screw jack or ball screw where you turn the screw/shaft to move the follower in a fashion to push a hollow piston. This would be similar to the worm and pall (fishing reel).
There is another type of traverse mechanism that uses only a twisted rod and follower. Turn the rod and follower advances.
The followers have to be made with a antirotation device.
I can see from your profile that you are a new member. Welcome to the fourm. However, in order to give you a proper answer, we will need more complete information about your application. As you can see, members have already devoted a lot of time to posting answers that are all over the map due to the lack of sufficient detail to work with.
Give us the details, and I am sure we can give your problem a real go.
MadMango,
Sorry I missed your post I think this is the way to go if he could reverse the rotary motion. This brings into play the worm and pall as posted by Dennyd. We had traverse mechanisms, but the longest I've ever seen is 24".
I'm try to find heidt a picture of the twisted bar.
It is similar to the child’s toy were you push down and the top spins.
Heidt,
The 3 inch pipe and 5 foot length would suggest a pair of pulleys with a drive belt / chain. It would depend if there is an amount of power that you need to transmit, or is it the position that needs to be the function. Besides the many v-belt and rubber belt products, there is a precision metal belt available,
, from a company with laser cutting / welding expertise. They use precision laser cutting to form pattern of drive holes in metal strip to make belts of almost any length. A clip weld attached to the belt would provide the linear motion. The 5 foot length would not be a challenge for the metal belt. You did not mention if there was a liquid inside the 3 inch pipe. The metal belts are usually stainless steel, but could be of other alloys for corrosion resistance. The thickness / width of the metal belt would be one of the limiting factors for power transmission.
heidt,
It appears that we assumed that axis of the rotary motion must be perpendicular to the linear motion. Is this correct or can the axis be in some other orientation?
Parallel, concentric?
Griffy
I've seen ad copy for an industrial version of the bait casting reel's level wind mechanism. Seems like the perfect solution for this problem. Self reversing, compact and fits into the package as described. Someone else must remember the company name?
All screw solutions and its derivatives, be them arquimides screws, twisted rods, helical cut groves, recirculating ball screws and rack & pinnion have the same requierement they have tu turn one way to go to one side and the other way to return, and that is not possible as been stated by HEIDT on the 27th so we have to fit a way of inverting the movement in a simple way with the motor allways turning the same direction.
I am thinking that using a simple or multiple lead screw with its nut turning alternatively one direction or the other by means of a friction disk clutch could do the trick.
Think how a friction press works, it has a central disk wheel that drives the nut and it is propelled by two perpendicular friction disks allways turning the same direction, one on each side of the center disk wheel, they come in contact one or the other with the edge of the center disk wheel and depending on the side that makes contact the ram (screw) goes in or out.
I don't agree. You can have helical cut grooves where the helix angle reverses at each end. The helix angle likely must be between 30 and 60 degrees to allow the follower to cross grooves successfully. I've seen this in application somewhere a long time ago but I can't remember what it was. Perhaps someone else has seen this?
Here is a picture of a traverse mechanism that would turn around if the motion was all in one direction.
The turnaround groove is the essential part of the mechanism.
I have a Stanley Yankee Handyman screwdriver - same idea. Funny you don't see them much anymore - used to be very common in the fifties and sixties - developed initially for production lines - but have been supplanted by electric and pneumatic screwdrivers.
Yes, Unclesyd's link is what several of us are thinking of... this type of levelwind mechanism self-reverses and could be contained within the cylinder described, IMO.
The follower or shoe rides in a helical groove cut in such a manner as to reverse axial travel at the end of the stroke without changing rotational direction.
The company I referred to earlier was Norco/Flennor. I may have been mistaken about the self-reversing feature of their product, however. Still, the product used followers positioned in helical grooves to obtain large linear travels from relatively small rotational input. Probably worth talking to them...
The levelwind mechanism I mentioned earlier seems to have gathered some support. I have one I modeled in SolidWorks several years ago. It is not to your scale but it could be a good starting point. The beauty of this mchanism is that it has a constant direction input, a smooth and quick direction reversal, and a (typically) uniform traverse speed. It is also very compact, but it does involve some geometry that folks aren't familiar either designing or manufacturing. The link provided by unclesyd should be a good starting point if you are really interested in this mechanism. A Skotch Yoke or similar mechanism will usually have a sinusoidal output for a constant input. What do you need?
As others have mentioned, you have a wealth of creative, experienced and willing contributors to this forum and this thread has grown long. You need to help us help you by giving more specifics of the problem you are trying to solve.
Adding to the post by Dennyd the mechanism is quite simple to make but becomes interesting to say the least in the design. The ones we used had all different traversing profiles, such as slow, speedup, slowdown, pause. All our traverse mechanisms were designed and built in house on a combination tracer and hydraulic milling machine. In most our mechanisms the worm was case hardened steel, the pall was made of nylon covered steel or bronze, the shoe had bronze bushings, some allowed a small adjustment pall position. All operated essentially 24/7/365 with very few problems.
I was checking on the design parameters when I was made aware that the designer, retired in 1990, of all the traverse mechanisms on site, sadly is in a nursing home.
No one at the site has his design expertise and his files and books were cleaned out because it was deemed he had nothing of value since he was a self taught machine designer and I might add a good one.
There should be current information on design as they are still used in some textile industry and as noted in the winch industry in place of fairleads.
Here is a better picture of different type cams.
Also note that they are called differents names.
Anecdotal:
The book he used for traverse mechanisms was small with a reddish cover and gold leaf edges on very thin paper pages, it looked like the old Audel Handbooks.
I propose we stop all the work until we know how much power has to be used, propelled or what ever with this device as we are all trying to put the tail to a donkey not only blindfolded but without knowing if there is even a donkey around.
Cheers,
SACEM1
I agree with strokersix just wonder if enough power can be transmited with so long a lead on the screw.
Hi Guys-
New member, first post:
What does the follower of a LevelWind Cam look like?
Can a levelwind work in high speed / High load applications with the right design?
Can a LevelWind Cam be used in low pressure angle desing i.e. <30deg?
Really would love to see a 3D design of a LevelWind and Follower!!
Pharoah72,
It called a pawl and has end cut to the radius of curvature of the inside dimensions of the worm or cam. They can be any length as long as it will pass over a slot without stopping or trying to enter the slot. The width is determined by load and amount of play that is acceptable.
