Anyone know a trick for tightening both head bolts at once?

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On my RF-30 clone, the bolts that tighten the head onto the column are a minor pain every time I have to change the head height. I can live with it, but I saw a clever way to tighten them both at once, by welding sprockets to the nuts and connecting them with a chain. Anyone else remember seeing that? I'm 98% sure it was a youtube.

I'm sure you've noticed, if you type "RF-30" or "Rong Fu" or "Round column mill" in Youtube you get dozens of videos, some of them of extremely poor quality, but a few gems. I was trying to find the one with the sprockets and chain for tightening the head bolts, but I seem to be only finding the bad ones where the guy never figured out that you can edit a video.

I'm thinking of trying it (the mill mod, not the video editing!) I'm sure I can work out the details myself, but if someone else has done it first, sometimes you can learn from it. If nothing else, they show you how NOT to do it.

I'm thinking three sprockets, with the third one in front of the back two. I'll power the third one with my cordless drill, with a gear reduction of 4:1 or more, smaller sprocket on the drill, bigger on the nuts, so it gets good and tight without too much force needed by my wimpy arm muscles.

It'd be awesome if someone here has done it, so I can benefit from your actual real-life experience, but I'll settle for speculation and crazy theories. Feel free to tell me if you think it's a dumb idea — save me from myself?

You may have seen my power Z-lift in the other thread, inspired by a couple youtubers (not my invention), works great! So I feel like I'm a whiz with chains and sprockets now, so I want to put them everywhere.




Thanks,

Mark in Seattle

 

[bulgie]

Avast that, no way I'm messing with chain and sprockets after seeing this: Cam-lock for both head bolts with one flip of a lever!

It's Italian, I think, I watched it with the sound off, didn't need any narration. It's brilliant, can't wait to get started.

 

[RJSakowski]

My particular flavor of RF30 has three bolts for locking the head. My procedure for tightening is to tighten the nut on the center bolt until snug followed by the lower and then the upper. Then I tighten the center nut to about 10 -15 lb-ft., followed by the lower and then the upper, I repeat the sequence, tightening to about 25 -30 lb-ft. Finally, I tighten to about 50 lb-ft.

I don't actually use a torque wrench; the numbers are for reference only. The reason for this sequence is to ensure uniform deformation of the casting. Tightening in a single action can distort the head casting which can slightly change the angle of the head. It also lessens the possibility of shifting the head in the process. My radial arm saw has a similar system for tightening and even though it has a key to keep it square, is is possible to clamp it slightly off square if not tightened with a similar sequence.

 

[bulgie]

My particular flavor of RF30 has three bolts for locking the head. My procedure for tightening is to tighten the nut on the center bolt until snug followed by the lower and then the upper. Then I tighten the center nut to about 10 -15 lb-ft., followed by the lower and then the upper, I repeat the sequence, tightening to about 25 -30 lb-ft. Finally, I tighten to about 50 lb-ft.

I don't actually use a torque wrench; the numbers are for reference only. The reason for this sequence is to ensure uniform deformation of the casting. Tightening in a single action can distort the head casting which can slightly change the angle of the head. It also lessens the possibility of shifting the head in the process. My radial arm saw has a similar system for tightening and even though it has a key to keep it square, is is possible to clamp it slightly off square if not tightened with a similar sequence.

Do you think your head needs 3 bolts? Given the 2-head versions out there seem to be reliable, maybe you could do without the middle bolt, at least strength-wise. Unless you think your casting is more light-duty, or shaped in a way that makes the middle bolt necessary?

Seems to me (with no evidence, just armchair theorizing) that if you tighten both bolts at the same time, that should preclude any weird cocking action, no? Just guessing but I'm imagining the distortion in the head that way as being pretty equivalent to tightening the middle bolt first on yours. Those cams in the Italian design are quite synchronized.

Your tightening sequence would drive me to drink I'm afraid. Life's too short! I hope that doesn't seem like an insult, none is intended. Your 40 years experience with the thing proves that your method is good. I'm just thinking for me, I could settle for a slightly "less good" procedure if it takes, say, one-fifth as long to do. Heck, this way looks to be faster than even picking up the socket wrench to tighten them the normal way. By the time you have the wrench in your hand, the cam-lock is ready to make chips.

I realize things aren't always as rosy as they look on Youtube, but the mod is reversible, no permanent changes to the mill.

 

[francist]

It will be interesting to see how the cam system works out, it looks very slick. I do wonder how long the axle for lack of a better word will last before it gets galled up but you never know. Disclaimer : I did quickly watch the video but not hugely in depth so I could easily be off base here.

In a way the idea is quite similar to another recent post by a member where they used a toggle system to tighten both knee gib bolts. I immediately thought of that but I don’t think it would have enough oomph for this application though, but you never know. It was pretty slick too but I’m unable to remember who posted it. It’ll come to me, or someone else will remember, it wasn’t more than a few weeks ago.

If you do go ahead with the cam affair, please make a stiffer handle. That wet noodle thing he’s got on there would drive me nuts!

 

[RJSakowski]

The advantage of the three bolts is by tightening the central bolt first, you will avoid the necessity of tightening two simultaneously. I never really thought about two vs. three. It came with three and that is what I use. I adjust the head height so very seldom that the process isn't obnoxious. It takes less than 30 seconds to tighten, even less to loosen and I'm not on the clock.

 

[bulgie]

If you do go ahead with the cam affair, please make a stiffer handle. That wet noodle thing he’s got on there would drive me nuts!

Haha yep, that bothered me too. I ordered some 3/4" 1144, though I might put a taper on it if I'm feeling fancy. Ball on the end?

 

[heli_av8tor]

In a way the idea is quite similar to another recent post by a member where they used a toggle system to tighten both knee gib bolts. I immediately thought of that but I don’t think it would have enough oomph for this application though, but you never know. It was pretty slick too but I’m unable to remember who posted it. It’ll come to me, or someone else will remember, it wasn’t more than a few weeks ago.

You may be referring to my post a few weeks back: https://www.hobby-machinist.com/thr...ou-make-in-your-shop-today.67833/post-1079531 Note that this idea is a compilation of several others work. It’s still working great.

It doesn’t have the oomph for locking the head and column. This cam lock device looks promising. I wonder what the equivalent tightening torque is?

 

[bulgie]

This cam lock device looks promising. I wonder what the equivalent tightening torque is?

The eccentricity of the cam (call it "E") is effectively your leverage. A less-eccentric cam could theoretically apply more force, but not if it runs out of travel before taking out the slop, the stretch of the bolt and compression in the casting. So it's a balancing act to arrive at the right amount of E. One approach would be to count how many turns of the nut it takes to go from loose to tight, and multiply turns by thread pitch (the inverse of TPI) to get the linear distance the nut travels. If your cam provides about that much travel and you set the starting point correctly, then the end point will be as tight as the nut. Assuming frictional losses are in the same ballpark as with threading a nut on. I have reason to believe friction will in fact be less than with the nut.

This design is well-proven if for no other reason than being the basis of almost all bicycle hub quick-releases (QRs). The first were designed in the '30s I think, and the design lasted practically unchanged into the 3rd millennium. The reason was they were so effective. A good QR can often secure the wheel better than an old-fashioned axle nut. Professional racers, with modern training and drugs, apply a huge amount of force when sprinting or climbing 25% grades. Snapping the drive chain is not unheard of, but wheels don't slip in the frame, providing the QR is done up properly — it is a skill you have to learn. But race mechanics used to get an entire wheel-change done in 10 seconds. Not exactly F1 pitstop speed, but this is by hand, tool-free, and tight enough for the world's top sprinters.

@francist asked bout durability: bicycle QRs are also well-proven there. I have QRs from the '50s and '60s (I'm a vintage guy) that still work like new. I can't remember ever seeing one wear out in fact. I don't know what steel they use though, or maybe it's the hard chrome plating? It's not like they didn't get used much; bike racers change wheels very frequently, sometimes taking the wheels off to transport the bike by car for instance, not to mention fixing punctures.

The cam surfaces that take the rubbing on this mill locking scheme are probably at least 5x, maybe 10x bigger than on a bike QR, so I'm hopeful that durability will be at least adequate. With galling in mind, I will try for good surface finish on the rubbing bits, and keep it lubed with high-pressure grease. Or would anti-seize be better in this application? It's not like a bearing that spins, it is immobile most of the time, then moves only a little and very slowly compared to say a spindle. So yeah, probably anti-seize.

 

[francist]

@heli_av8tor Yup that's it, thanks for putting in the link. I tried searching for it but for the life of me couldn't find it again!