Rotary motion to reversible linear motion

olf20 · Feb 11, 2025

I'm not totally happy with the way motion is transferred from the steel pressure plate to the final drive shaft via the rubber o-ring, so am making up a couple of compression spring holders to hold compression springs against the final driveshaft bearings to hold a more constant pressure between the rubber o-ring and the steel pressure plate.----Brian

All the snow blowers that use this type of drive use a lever and operator to apply
the pressure to the two. But they do work great for a long time, not to mention you
get reverse as a bonus.
olf20 / Bob

Brian Rupnow · Feb 12, 2025

What did I do today?--Well, not that much really. Since I am now going to put roller bearings on the shaft that meshes with the rack to drive the carriage back and forth, I had to make a new gear which gets locked to the new hardened shaft. (The old gear and shaft were machined from one piece of mild steel.) I like this gear better--the outside diameter of the first gear was not perfectly concentric to the bore, so it had a hard spot in it when the rack travelled full length. I haven't decided yet whether to make the new shaft from a piece of 1045 steel and leave it unhardened (but harder than mild steel) or to make the new shaft from 01 steel and harden the areas where the bearings ride on. Problem is, there's a keyway milled down one side of the shaft, and I don't know if the shaft will remain straight after hardening or if it will "banana" on me because of the keyway.

Brian Rupnow · Feb 13, 2025

Today I picked up my B68 roller bearings from Koyo, bored out my brass pillow block bearings, and pressed the Koyo bearings into place. So far, so good. Now I have a question, and all of my machinists who I used to ask questions of are now retired, so I will ask on here. I know that the roller bearings will gall a mild steel shaft. (There is no inner race). I have three types of shafting available to me, mild steel shaft, 4140 shaft, and 01 shaft. There is a 1/8" wide x 1/16" deep keyway cut down one side of the shaft. I could make the shaft from 01 steel, then flame harden and quench the areas that the bearings ride on. Only thing is, with that keyway down one side of the shaft I am afraid that the shaft will go "banana shaped" when I do that. I don't want to use mild steel shaft because, as I said, the bearing rollers will gall it. I have a piece of 4140 shaft that seems to cut just fine using a carbide tool in my lathe. I could use the 4140 shaft, in it's unhardened state, as I purchased it, but I don't know if the bearings will gall the 4140 shaft in it's unhardened state. I'm open for suggestions and hope to here from someone who has experience. ---Brian

Sparky_SC · Feb 13, 2025

If it is 4140PH (prehardened) I would go with that. The prehard version is very common so I would not be surprised if that is what you have. It machines well even though it is around Rc 35-40. 4140 annealed would also work for this application.

I wouldn't try hardening the o1, I think that would cause issues. The surface finish on the shaft is just as important as the hardness, perhaps even more.

In your application I doubt you will ever have enough load or run time to ever cause any problems. I would just polish up the bearing area on the shaft to a mirror finish. If it was for something like a car transmission my reply would be quite different.

dsage · Feb 14, 2025

I worked on a lot of machines that used bearings like that and the shafts (although stainless because of the environment they were used in only) were not hardened. The shafts were easily machined so not hardened.
Just be sure the shaft is dead-nuts the proper diameter and (as mentioned) polish it to a mirror finish. There are so many "bearings" in there the load on any one will be minimal.
Also - are those really considered rollers or needles??
SO IMHO I say don't waste the effort to harden the shafts.

TonyM · Feb 14, 2025

dsage said:
I worked on a lot of machines that used bearings like that and the shafts (although stainless because of the environment they were used in only) were not hardened. The shafts were easily machined so not hardened.
Just be sure the shaft is dead-nuts the proper diameter and (as mentioned) polish it to a mirror finish. There are so many "bearings" in there the load on any one will be minimal.
Also - are those really considered rollers or needles??
SO IMHO I say don't waste the effort to harden the shafts.

Needle rollers as opposed to "Roller bearings" which have rollers only a bit longer than their dia. Same as used on propshaft UJ's. I understand trying to keep the OD as small as possible but it seems a bit overkill on a model. A polished unhardened shaft with modern bushing will probably outlast anything with rollers.

roncohudd · Feb 14, 2025

Brian Rupnow said:
Today I picked up my B68 roller bearings from Koyo, bored out my brass pillow block bearings, and pressed the Koyo bearings into place. So far, so good. Now I have a question, and all of my machinists who I used to ask questions of are now retired, so I will ask on here. I know that the roller bearings will gall a mild steel shaft. (There is no inner race). I have three types of shafting available to me, mild steel shaft, 4140 shaft, and 01 shaft. There is a 1/8" wide x 1/16" deep keyway cut down one side of the shaft. I could make the shaft from 01 steel, then flame harden and quench the areas that the bearings ride on. Only thing is, with that keyway down one side of the shaft I am afraid that the shaft will go "banana shaped" when I do that. I don't want to use mild steel shaft because, as I said, the bearing rollers will gall it. I have a piece of 4140 shaft that seems to cut just fine using a carbide tool in my lathe. I could use the 4140 shaft, in it's unhardened state, as I purchased it, but I don't know if the bearings will gall the 4140 shaft in it's unhardened state. I'm open for suggestions and hope to here from someone who has experience. ---Brian

Find a piece of cold rolled and it will work very well.it is natural grade 5 same as bolts.i have made lots of agricultural shafts from it.

Brian Rupnow · Feb 16, 2025

I never had good luck running roller bearings with no inner race on a cold rolled shaft. I have come up with a solution which lets me use a cold rolled shaft but hardened 01 bushings in the area where the bearings will ride. The bushings were heated to a dull cherry red, then quenched in oil, then "drawn back" for two hours at 400 degrees F to make the bushings tough and less apt to shatter.---Brian

Brian Rupnow · Monday at 6:31 PM

Today there was success. After much faffing about, I was able to turn the gear reducer by hand, which by way of three o-ring drive belts turned the primary driveshaft with the small bevel gear on it. This small bevel gear mated with the larger bevel gear and caused the rubber o-ring friction wheel attached to the driveshaft with the gear on the end to rotate, driving the carriage either forward or backward depending on which position I had the reversing handle in. Wow, that's a lot to say!! I did use a larger o-ring going from 1/8" cross section up to a larger (3/16") diameter o-ring for the friction wheel. Nothing in life is easy---I had to make a different hub to hold this larger o-ring, and due to the nature of the beast I ended up having to completely dismantle the final drive shaft, install the larger steel hub, and then reassemble everything. Tomorrow I will finish up the two fixtures which hold some spring tension on the shaft with the rubber friction o-ring on it.---Wish there was a course on TIG welding at the local college, but the tig welding is rolled into a course that covers about four different types of welding. The only remaining uncertainty is whether the engine has enough power to drive everything. I believe that the large gear reduction I have set up with my o-ring drive belts will be sufficient to let the engine drive this set up.

Brian Rupnow · Wednesday at 7:26 PM

Today I built and installed the spring tension fixture which bolts to the end of the fixture holding drive and driven shafts . It guarantees a good pressure between the friction wheel and the rubber o-ring on the geared driveshaft.

Rotary motion to reversible linear motion

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