Cutting Threads in Carbon Steel

[M J D]

I might put more than two. I would TIG weld it and use spaced out stitch welds (4-5?) and in this case some 309 or 312 filler. The trick is to be positive about the alignment before welding and don't give it enough heat to warp too much

It's not rocket science, once it's aligned tack it on there. No real need for any special filler as sprockets, even hardened ones are nothing special, if they are hardened it's a surface hardening on the teeth.

[GoK4rtFanatic]

To give some context. I am "engine-swapping" an electric razor dirt bike (the mx650 model). I am new to electrical work and much more comfortable working on engines and less complicated parts to keep this as simples as possible. That being said, I have decided to run a jackshaft where the electric motor used to live. In its place, I will run a 3/4 inch axle shaft mounted on two pillow block bearings (due to it being a full suspension frame, I will need a chain tensioner). The axle shaft I plan to run is a 1566 carbon steel shaft that needs to be no longer than 10-12 inches. It is a 3/4 inch diameter shaft with a yield strength of roughly 70,000 pounds, so I am not worried about the tapped holes having mechanical failures. I can see why welding it is a good option, however, I would have just bought normal sprockets if I wanted to do so. The entire idea behind my set screw design is to allow for as much adjustment as possible. In my previous experiences, I have struggled with adjustments using a keyway, as they tend to rust or collect dirt and then clog up. Essentially it is a shorter version of a go kart shaft (it consists of two sprockets run on one shaft spaced around 8 inches apart, with the intent of transferring the power of the motor from the left side of the bike to the right side where the OM drive sprocket is attached to the wheel). Is it more complicated than it needs to be? Absolutely, however with this system, I am allowed a much greater ability to tune each piece. I have purchased around two feet of the rotary shaft with the intent to have a backup piece and/or have a piece to test various taps and fasteners. All this being said, it is a small 50 cc husqvarna engine, the bike is small, and much lighter than a go kart. Space constraints are an issue, and this method, while way more complicated than it needs to be, is space saving.


Other important details

The set screws are 90 degrees apart
The axle has pretty high tolerances
The pillow blocks are rated for high rpms
I am running #25 roller chain to keep sprocket diameter low
I have a tabletop drill press, assorted measuring tools, clamps, welding equipment (that I would prefer not to use)

[M J D]

I might put more than two. I would TIG weld it and use spaced out stitch welds (4-5?) and in this case some 309 or 312 filler. The trick is to be positive about the alignment before welding and don't give it enough heat to warp too much

To give some context. I am "engine-swapping" an electric razor dirt bike (the mx650 model). I am new to electrical work and much more comfortable working on engines and less complicated parts to keep this as simples as possible. That being said, I have decided to run a jackshaft where the electric motor used to live. In its place, I will run a 3/4 inch axle shaft mounted on two pillow block bearings (due to it being a full suspension frame, I will need a chain tensioner). The axle shaft I plan to run is a 1566 carbon steel shaft that needs to be no longer than 10-12 inches. It is a 3/4 inch diameter shaft with a yield strength of roughly 70,000 pounds, so I am not worried about the tapped holes having mechanical failures. I can see why welding it is a good option, however, I would have just bought normal sprockets if I wanted to do so. The entire idea behind my set screw design is to allow for as much adjustment as possible. In my previous experiences, I have struggled with adjustments using a keyway, as they tend to rust or collect dirt and then clog up. Essentially it is a shorter version of a go kart shaft (it consists of two sprockets run on one shaft spaced around 8 inches apart, with the intent of transferring the power of the motor from the left side of the bike to the right side where the OM drive sprocket is attached to the wheel). Is it more complicated than it needs to be? Absolutely, however with this system, I am allowed a much greater ability to tune each piece. I have purchased around two feet of the rotary shaft with the intent to have a backup piece and/or have a piece to test various taps and fasteners. All this being said, it is a small 50 cc husqvarna engine, the bike is small, and much lighter than a go kart. Space constraints are an issue, and this method, while way more complicated than it needs to be, is space saving.


Other important details

The set screws are 90 degrees apart
The axle has pretty high tolerances
The pillow blocks are rated for high rpms
I am running #25 roller chain to keep sprocket diameter low
I have a tabletop drill press, assorted measuring tools, clamps, welding equipment (that I would prefer not to use)

Another option may be to use split shaft collars to grip down on the shaft. You could weld a portion of the collar, opposite the split, to the sprocket. If I understand correctly, you want to thread a set screw thru the sprocket then into the shaft? Can't see that working well as you will never obtain a " tight" connection that way as the threads won't allow that.

[GoK4rtFanatic]

I'm still a bit confused on how it won't be a "tight" fit. It works the same way as a set screw normally does. It will thread into the shaft and jam against the bottom of the tapped hole, same as if there were no hole and it was just tightened against the shaft. The tapped hole is unnecessary, a drilled hole about 3/16 yields a similar result. To make it more clear, I don't plan to thread the set screw in the full length. The hole that I make will only go about 3/16 in down into the shaft, where it will then be tapped. The set screw is then fully tightened down, and 1/8 (2/16 in of the 5/6 in set screw) will remain in the OM threaded hole in the sprocket. To deal with any loosening that shaking or vibrating may cause, I could use thread locker or better yet, a set screw with a nylon patch to dampen the effects. Essentially I am just using the set screw as a bolt to hold two tapped pieces together. The tapped hole is a blind hole and as such, the set screw will touch the bottom of the hole with 1/8 of the set screw still in the sprocket hub. The thing is, I could use press-fit pins to do essentially the same thing. Because the two pins (or set screws) are 90 degrees apart, it makes it impossible to detach the sprocket without first removing the pins, or breaking another piece in some way. By that same logic, I should be able to use set screws the same way, but relying on threads instead of a press-fit. I really would rather not weld this together.

Another way to think about it is taking two pieces of flat bar. Then drilling and tapping a hole through both of them. In this hole, you thread in not a bolt, but a threaded rod. Of course, just by turning one of the pieces, the piece would slowly unthread itself from the rod. If you were to drill a second hole and tap it as well, you would notice that the problem with the piece being able to turn and unthread is no longer an issue. I am applying this logic to different pieces, but same concept.

[Meltedmetal]

You seem to misunderstand what people are saying. A normal set screw application where a set screw is screwed against a shaft, in a hole or just against the shaft will pull the sprocket hub against the opposite side of the shaft removing the play that allowed you to slip the sprocket onto the shaft. 2 set screws work even better. What you are proposing will set the screw firmly in the shaft but will not eliminate any other clearances and will not tighten the sprocket hub against the shaft. Your assembly will drive exclusively on the set screw without any additional friction against the shaft because it will not pull the hub to the shaft. Clear as mud, right?

[GoK4rtFanatic]

Okay starting to make sense, I think. Certainly running a 1/4-20 socket cap screw at the right length would work in place of a set screw though, no? Same concept, but the screw head would protrude from the sprocket hub for easy tightening, and the hex part would drive the sprocket down instead of away like a set screw would on a normal shaft. Obviously set screws work with the principle of pushing the sprocket away to jam down on the shaft, but a bolt works the other way, and would pull the sprocket down when tightened.

[M J D]

Okay starting to make sense, I think. Certainly running a 1/4-20 socket cap screw at the right length would work in place of a set screw though, no? Same concept, but the screw head would protrude from the sprocket hub for easy tightening, and the hex part would drive the sprocket down instead of away like a set screw would on a normal shaft. Obviously set screws work with the principle of pushing the sprocket away to jam down on the shaft, but a bolt works the other way, and would pull the sprocket down when tightened.

Correct. Drilling a shallow 1/4" dimple in the shaft and using the setscrew accomplishes the same. Problem is your still relying on a small portion to prevent the sprocket from twisting on the shaft. A keway with an appropriate key provides much more material that would need to shear before the sprocket would turn on the shaft.

[farmersammm]

Could you please explain what you mean by drilling the sprocket?

Place the sprocket on the shaft where you want it, then drill a hole through the set screw hole on the sprocket, keep drilling through the shaft to the other side, and continue drilling through the other side of the sprocket. Get a bit that will completely, or mostly, remove the threads in your starter hole.....this will insure that the bolt will be tight without slop. I guess it's at least one way to skin the cat, and is far stronger than trying to secure the sprocket with just a few set screws.

[Meltedmetal]

Okay starting to make sense, I think. Certainly running a 1/4-20 socket cap screw at the right length would work in place of a set screw though, no? Same concept, but the screw head would protrude from the sprocket hub for easy tightening, and the hex part would drive the sprocket down instead of away like a set screw would on a normal shaft. Obviously set screws work with the principle of pushing the sprocket away to jam down on the shaft, but a bolt works the other way, and would pull the sprocket down when tightened.

If I am understanding what you are saying not really. If you drill all the way though like Sammm is saying, you won't pull the sprocket against the shaft at all because you can't compress the hub. For what you are driving I doubt it would make any difference. Like Sammm said earlier the bolt would be like a shear pin. Every farmer knows all about shear pins. For sure in my opinion MJD's suggestion of a key(I would use a woodruff key)and secure the sprocket in place with the set screws would be the best but you may not be equipped to cut the key slot.

[Boostinjdm]

What you're making is a typical mini-bike or go-kart jack shaft. It's not rocket science and the normal connection methods are a woodruff or straight key in a pocket to take the load and the set screws to keep it there. What part of the country are you in?

[M J D]

Drilling a 1/4" hole thru a 3/4" shaft certainly won't help with the strength of the connection. Might as well saw halfway thru the shaft while your at it

[ferrret3238]

I would recommend a keyway and a taper lock. I believe you stated a 3/4 shaft and a 2-1/2 outside of the sprocket so I'm assuming # 40 chain and about 16 tooth sprocket. This would be in the realm of a QD taper lock. They grip shafts really well and i have never had one break loose on anything that i have seen them on. If you're really worried about something walking on the shaft a split collar would be some insurance for that.

[Boostinjdm]

I would recommend a keyway and a taper lock. I believe you stated a 3/4 shaft and a 2-1/2 outside of the sprocket so I'm assuming # 40 chain and about 16 tooth sprocket. This would be in the realm of a QD taper lock. They grip shafts really well and i have never had one break loose on anything that i have seen them on. If you're really worried about something walking on the shaft a split collar would be some insurance for that.

This is going to be too small for taper lock. He already stated a #25 chain. That combined with the motor choice means he's going to need about as small of a sprocket as he can get. I had to get a one piece sprocket/hub for my mini bike. Can't remember if it was 10, 12, or 14 teeth, but that was for #40 and they were only 1.5" or so diameter. I bought a few to try. I think I only used a 5/8" shaft too.

[albrightree]

Taper lock, QD bushing, key/setscrew, setscrew/divot/Dshaft, roll pin, press pin, are all commonly used methods to attach sprockets to shafts. Welding is a last ditch sort of thing. It will be harder to line up the tapped holes than you think. If you don't drill and tap together the might not thread up right, or at all. I think a lot of us have done this before somewhere, and know that its more work, and will lead to not as good a fix.

this says it better than I can : https://www.physicsforums.com/thread...readed.644648/

a slotted 5/16"x 1 1/2" spring pin is rated for 10,000 pounds(https://www.mcmaster.com/98296A941/)
and is $12.15 for 50 pcs,

Should be sufficient as you #25 chain is probably rated for less than 200 lbs.

https://www.mcmaster.com/6261K171/

[GoK4rtFanatic]

Welding is a last resort for sure. I understand that a key way or woodruff is recommended. I knew that before I bought the parts. The entire point of this project was to accomplish what a key way would without a key way. I have had poor experiences with key ways in the past, and wanted something a bit more simple. Obviously the process to get to that state is more complex. To those saying that ain’t am unable to tap through it without severely weakening the piece, I must disagree with you. Normally I would have to agree, But this rod is heat treated and meant for applications at much higher load. Not only that, but the stress failure would be nearly impossible due to the point of failure that it would have to occur at. I think I will just end up drilling a couple of holes for the set screws to rest in. There is gonna be some trial and error, but essentially I would drill it to where the set screw prevents lateral and forward movement. So am I wrong to think that if I just drill a hole about 3/16 in deep in the shaft, leave it unthreaded and slide the sprocket on and tighten the set screw in, it will work like a set screw normally does, but it would also prevent side-to-side and backward-forward movement?

[farmersammm]

Might work if you swap out the set screw for a regular hex head fastener that is long enough to fully engage the thread in the sprocket.

[farmersammm]

Using the blue Locktite would hold it I'd imagine........keep it from vibrating loose. Red holds better, but is a PITA to get loose. Although.........if you don't mind heating the part to around 400*, it will release just fine when using Locktite.

[farmersammm]

Shame you don't have a mill. Have you checked how much it would cost to cut a keyway?

My swather (used to cut hay) has a 14' reel that moves the crop into the cutting bed, and it's run by a rather small sprocket on a 1" shaft(maybe 1 1/4" been a while since I've worked on it). It's held on by a gib key, and it's running a pretty hefty load, with considerable input power from a good sized hydraulic motor.

the pic shows a standard key.....I was only checking fit after I milled the slot.

[farmersammm]

https://www.ebay.com/itm/16210341655...79c00f7075fbd8

[Louie1961]

https://www.ebay.com/itm/16210341655...79c00f7075fbd8

Sammm for the WIN!!

[Oldiron2]

Using the blue Locktite would hold it I'd imagine........keep it from vibrating loose. Red holds better, but is a PITA to get loose. Although.........if you don't mind heating the part to around 400*, it will release just fine when using Locktite.

I didn't read all the posts on this second page, but didn't think the OP's situation was putting that much torque on the shaft. Keys, welding, etc. seem like overkill. I second Sammm's suggestion of applying Locktite, then tightening the setscrew(s), and letting it cure well before use.

[mla2ofus]

how about drilling a countersink in the shaft. Then use 2 setscrews, one to anchor in the shaft and one one on top of the first to prevent it from backing out.

[GoK4rtFanatic]

I agree with the locktite idea, but why countersink?

[mla2ofus]

, but why countersink?

So it can't turn on the shaft.

[Oldiron2]

I agree with the locktite idea, but why countersink?

Often, a small depression is useful for a tight-fitting sprocket so that tightening the setscrew doesn't raise a ridge that interferes with the sprocket removal later. A depression also increases the shear force needed to get the screw to turn on the shaft, although a good application of Loctite, with the great surface area between the shaft and sprocket, should make that less significant here.