Looking for: Vee thread based worm wheel

I'm guessing here:

I think that such an assembly would be even more inefficient than a worm drive. Additionally, it seems that getting proper mesh would be problematic: a worm gear will have a sort of flat-ish spot that'd give you a nice broad optimum, while a V-cut would require that you get everything just right to work. Moreover, the V-cut would tend to always want to push the gears apart, to a greater extent than a normal worm gear tooth profile -- put that together with the extra need for accuracy, and it'd be difficult to keep your assembly in tune.

It sounds like one of those deals that's just too good to be true.

Jon Anderson fired this volley in news:vi7Cq.101762$ snipped-for-privacy@en-nntp-14.dc.easynews.com:

Jon, I don't remember the company, but I saw a neat demo either here or on CNCzone that showed a guy making such wheels.

He pivoted the blank on a shaft on a vertical member in his mill vise, then used a common tap of the requisite thread as a milling tool. He simply advanced the tap sideways into the edge of the blank a few thou, and let it cut all the way around, then advanced again, etc., until the profile was cut full depth.

It was simple, elegant, and worked perfectly.

LLoyd

I've made several of these things on my lathe with the milling attachment. One of them is in use right now, on my fishing-rod rotisserie, which I use for getting the layer of epoxy evenly distributed on guide windings.

If you're in need of a light-duty worm gear, they work fine. You chuck an ordinary thread tap in the lathe spindle. First turn a blank for the gear in the lathe, drilling and boring a hole in the center for a temporary spindle.

I've used a bolt for the spindle, polishing it up a bit on the lathe. Chuck the spindle with gear blank in the milling attachment vise (you can clamp it in a toolpost if you don't have a milling attachment). Feed the edge of the gear into the rotating tap until it starts to cut. It will self-feed.

If' you're lucky, it will cut clean, or nearly so, all the way around the blank. If it's a little rough, keep feeding the blank into the tap until you get a clean cut. You may have to turn a little bit off of the blank's periphery to get a clean cut all the way around.

That's all there is to it. If you need an exact number of teeth on the gear, forget about it. d8-)

Yeah, that's the technique I'll be using if I end up making it.

The intended use btw, is a vertical column for my macro photography rig. I'm big into recycling what I got, and I happen to have a Sherline Z slide. I'll use a different screw with a RH thread. The worm wheel will have a knob at the end of it's shaft and when this knob is turned, it'll act like a rack and pinion. When this shaft is locked, I can use the screw for fine adjustment. Loads will be very light and use rather infrequent really. I hesitated to mention intended application as that just invites a lot of input on other ways to do things. I have a lot of options and I know what they all are. But I like to do things a bit different. I know what I'm doing and why I'm doing it and not really open to debate. (however, if someone has a focus block like the vertical one pictured below they would sell REALLY cheap, I'd jump on that!)

Overall, this is more or less what I'm building:

Except I'm using linear slides instead of expensive focusing blocks for linear movement. And the slide my bellows/camera mounts to will be driven by stepper motor via a dedicated and purpose built controller.

Jon

You are right. But for my ultra light and infrequent application, not an issue.

Jon

Here is Chris Heapy's procedure:

Kevin Gallimore

Not so much giving you an input on other ways...............Well yes it is, but then..........

Can you not use a regular worm gear and Acme threaded rod with the same pitch?

Dan

Don't see why not, but I'm looking to either use as much as I can from my scrap and parts bins, or buy something that'll do the job. If I have to go buy acme screw stock and a worm wheel and add labor to that, I'm getting close to the tipping point of just buying a focusing block. If I could get a post mount focus block for $50, I'd just do that, but cheapest I've seen one on ebay is around $90. Spend money and save labor or spend labor and save money. Don't want to do both... And, I do like the idea of doing something a bit different...

Jon

V ? Most threaded rod is a V.

I think you wanted the square based thread used on lathes and mills. A flat end screw rides in it or a half nut clamps on them.

Either a square thread or an Acme screw thread (most common).

MSCdirect also has screws.

Greetings Jon, I have made for myself several worms and wormgears using the tap method. If you decide to go this route use a high spiral tap if you have one. These taps stay engaged in the work constantly. I have had no trouble getting the exact numbers of teeth I wanted. I have used

3/8-16, 5/16-18, M8 x 1.25, and other taps of similar size but different pitches to cut the wheels. I just hold the tap shank in a collet. The wormgears (AKA wormwheels) I held with a screw screwed into a piece of steel stock held in a toolholder on the Aloris toolpost. Making the gears out of brass is easy and I bet you could make your first one in less than 1/2 hour. Eric

Excellent tip on the high spiral tap, thanks for that!

Jon

No, I want a V based worm. As mentioned, I know what I want and why I want it. It's a very low stress application. I like designing things that work a bit different. Also known as, I enjoy being a weirdo sometimes...

Actually I'd use acme rod if I had any suitable acme taps laying around. But the cutting of light duty vee thread worms is not all that uncommon. There is a fellow not too far from me that makes tracking mounts for telescopes. He uses V thread based worms. If it's good enough for telescope use, it's good enough for me!

Jon

Well, not trying to be snotty toward everyone telling me I really want an acme thread, but I did find it annoying to clearly describe what I wanted and why I wanted it, and still be told that's not what I want. I know those folks were trying to be helpful.

So I grabbed a box of misc gears, found a small SS pinion that seemed to roll nicely over a 3/8-16 tap. Took all of 15 minutes to hack up a really crude 'hobbing' fixture and 'hob' the gear. It rolls very nicely up and down a 3/8-16 thread as a rack and pinion. When the gear is locked, it'll act like a nut, allowing fine adjustment.

I WILL post pictures of this setup when done, as well as a shot of the 'hobbing' setup. It's now a done deal, I just have to finish my brother's macro rig so I can start on mine...

Jon

Ok, here's a couple quickie shots. It's rude, crude, and ugly. And it'll do exactly what I want. Therefore in my eyes, it's beautiful!

Should have just done it and been done with it. The manufactured version of what I originally asked about probably would have cost more than I wanted to spend anyway...

Jon

Very nice, Jon. Man, that gear is tiny, relative to the pitch of the worm. Your ratio is down around what you would expect to get from regular bevelled gears.

I'm assuming that you want the binding effect that prevents the gear from driving the pinion? Or you're looking for more smoothness than you can get with ordinary-quality bevel gears?

Or what?

Ok, full description:

As I mentioned in the original thread, I wanted a focusing block that mounts on a round shaft, but haven't found any in my price range. The Sherline Z slide offers all the vertical travel I need. I was just going to use the column as-is until I realized it would be rather slow to run it up and down it's full range.

I'll make a new thrust plate at the top to move the screw away from the column a bit. It will pass through a closely fitted hole in a block that is also fastened to the back of the Z slide.

90 degrees to this screw, will be the gear I just hobbed, on a shaft, with a knob at one end. There will be a provision to clamp this shaft.

When the vertical screw is stationary and the gear's shaft unlocked, it will allow raising and lowering the slide just like a rack and pinion.

When I lock this shaft and rotate the vertical screw, it will function just like the original screw, allowing for finer adjustment. To sum it up then, it will function as both a pinion on rack, and a leadscrew w/nut.

My brother, having more $$ to spend on his rig, is using a crossed roller slide with micrometer head for fine adjustments, mounted to a post for course adjustments. I have a lower budget for my rig and was looking to use stuff I have on hand (the Sherline slide). I'm also probably not going to be working at the extreme magnifications he's going after and a 3/8-16 thread will offer sufficiently fine control.

The gear rolls over a 3/8-16 bolt just as smoothly as a regular pinion over a rack. I chose it as it rolled over the tap almost as smoothly before hobbing.

I'll post pics when done, but that will be well into next year. Still have a lot of work to do on my brothers setup.

Jon

You're welcome. Eric

I was not trying to say that you really wanted an Acme thread. But if you could not find the vendor of Vee worm wheels, you could use a common worm wheel with an Acme threaded rod.

Dan

Dan,

That was directed more at posts suggesting what I was trying to do wouldn't work well. And they would be right if any significant force was to be transmitted. All in all, maybe I should have spelled out the details up front. But there's usually a naysayer that will pipe up anyway, that's the nature of usenet. My problem is I feel compelled to explain everything instead of ignoring them.

I wasn't sure I could get a worm wheel that would run on standard Acme threaded rod, but one thing that made me think of the vee worm wheels was the claim they were significantly cheaper than a proper worm wheel. Of course, hobbing a gear that's been sitting in a box for the last 20 years with a tap is cheaper yet. I'm not exactly McGyver, but I do enjoy figuring out how to do what I want to do using as much as possible, bits and pieces I have laying around. And I have lots of bits and pieces laying around...

Jon