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DFX file
- Thread starter DPittman
- Start date
DPittman
Ultra Member
Prepare to laugh..... I use an old l.p. vinyl record (Blue Oyster Cult" lol) with a glued on index template and attach that to the lathe spindle. I use a simple pointer in a magnetic stand to indicate the position. The large diameter of the record allows for pretty good accuracy and it works amazingly well. The only big down side is I do not have any mechanism to lock the spindle in place. So far that hasn't been an issue but it would be immensely better if I could lock it down.
From what I've been able to piece together on the engine, its not a planetary cluster so that eliminates a lot of headaches. So if you could find an internal gear of the correct size & a reasonably priced spur gear cutter to match, then you would be set? I don't think there is anything magical about 72. The internal could be 60 using a 30 tooth spur for example. Is that a reasonable starting point?
https://www.homemodelenginemachinist.com/threads/elmer’s-5-geared-engine-maybe.30206/page-2
This is what I’m going on. I don’t feel that the size of the ring gear is all that critical. As long as it has an even number of teeth and the orbiting gear is half the size it should work. Then so long as the holes in the gear arm set at half the diameter of the orbiting gear this will put the piston rod screw running along a line with the center of the crank shaft. In this drawing the diameter of the gear could be 2 inches of 2 feet and the geometry stays the same. It would have to fit within the envelope of the engine of course.
Here is a complete planetary gear assembly for a clutch as an example of harvesting ring gear if you still wanted to make the spur gear
https://www.aliexpress.com/item/400...chweb0_0,searchweb201602_2,searchweb201603_55
Internal gears are kind of spendy, IMP or MOD because they are not trivial to make. Looks like if you can accept a thicker tooth, the price goes down. Easier to make as well. Lots of spur gears are available cheap in teh RC world. I've seen DP but I would expect module is more popular. Hopefully there is a combination solution in there somewhere.
https://shop.sdp-si.com/catalog/?cid=p203
https://www.homemodelenginemachinist.com/threads/elmer’s-5-geared-engine-maybe.30206/page-2
This is what I’m going on. I don’t feel that the size of the ring gear is all that critical. As long as it has an even number of teeth and the orbiting gear is half the size it should work. Then so long as the holes in the gear arm set at half the diameter of the orbiting gear this will put the piston rod screw running along a line with the center of the crank shaft. In this drawing the diameter of the gear could be 2 inches of 2 feet and the geometry stays the same. It would have to fit within the envelope of the engine of course.
Here is a complete planetary gear assembly for a clutch as an example of harvesting ring gear if you still wanted to make the spur gear
https://www.aliexpress.com/item/400...chweb0_0,searchweb201602_2,searchweb201603_55
Internal gears are kind of spendy, IMP or MOD because they are not trivial to make. Looks like if you can accept a thicker tooth, the price goes down. Easier to make as well. Lots of spur gears are available cheap in teh RC world. I've seen DP but I would expect module is more popular. Hopefully there is a combination solution in there somewhere.
https://shop.sdp-si.com/catalog/?cid=p203
You have to share an image please. We have a closet full of LPs and I need an indexer. What better use for a Partridge Family record
Also an PDF of your index template, please.
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trlvn
Ultra Member
Somewhere on YouTube, there was a 10 inch table saw blade used as an indexer. You make a pin that will lever into the tooth gullet (snugly). Saw blades come in a variety of tooth counts and even if the teeth are damaged they still make a good index plate. FWIWYou have to share an image please. We have a closet full of LPs and I need an indexer. What better use for a Partridge Family record
Craig
DPittman
Ultra Member
It was already mentioned that a circular saw blade can be used...I also have seen a lathe gear used and that has the advantage of an easier mechanism to lock the spindle in place using the gear notches/spaces. Several other ways this can be done as well. I used the vinyl record method because really what else would a "Blue Oyster Cult" LP be good for other than a clay pigeon or frisbee?You have to share an image please. We have a closet full of LPs and I need an indexer. What better use for a Partridge Family record
Attachments
DPittman
Ultra Member
Well I'm getting closer..... I ended up grinding a 3/16" hss tool bit to very rough shape on the 8" bench grinder but then moved to grinding it under a microscope with a .040" diamond bit in a dremel tool. Grinding a bit under a scope takes some getting use to but it wasn't as bad as you might imagine. I was hesitant to do so because the thought of the dust on my microscope made me ill, but as it turned out there was very little dust. A bit of trial and error but I used dykem and sharpie ink and that helped me see where I was grinding or high/low.
I broached a few teeth in a delrin blank to see what sort of fit I would get. I used my brass external gear to test and I think the fit may be good enough to move on to trying an internal gear in brass. My haywire methods and setup sure leaves alot of potential for errors but I may be able to live with the results. The size of module 0.5 teeth and the tiny tool bit means that .010" error is significant.
I broached a few teeth in a delrin blank to see what sort of fit I would get. I used my brass external gear to test and I think the fit may be good enough to move on to trying an internal gear in brass. My haywire methods and setup sure leaves alot of potential for errors but I may be able to live with the results. The size of module 0.5 teeth and the tiny tool bit means that .010" error is significant.
I admire your perseverance! I've seen large screen machinist projectors used to verify geometry & probably still how its done, maybe digitally I dunno. Anyways microscope should be same principal, just at the other end of magnification.
Not sure if you checked in on your HMEM post but the one fellow is suggesting the resultant ring gear DXF profile looks a bit iffy. Its so hard to make out because the tooth & gap drawing profile is so small with only 0.5 mod. But the kind of bothersome detail is the program doesn't have inputs that would normally be associated with ring gear design. So what does that mean? Trust that he did it right? Or maybe he didn't do it quite right? In other words, I would hate to see you painstakingly replicate the DXF gap making a single point broach, only to find it has built in clearance issues because the software took a shortcut. I guess you will find out soon enough. For a low load application like what you are doing I will bet money you will get it to work. Now if you were replacing a gear in your transmission... maybe not LOL.
Not sure if you checked in on your HMEM post but the one fellow is suggesting the resultant ring gear DXF profile looks a bit iffy. Its so hard to make out because the tooth & gap drawing profile is so small with only 0.5 mod. But the kind of bothersome detail is the program doesn't have inputs that would normally be associated with ring gear design. So what does that mean? Trust that he did it right? Or maybe he didn't do it quite right? In other words, I would hate to see you painstakingly replicate the DXF gap making a single point broach, only to find it has built in clearance issues because the software took a shortcut. I guess you will find out soon enough. For a low load application like what you are doing I will bet money you will get it to work. Now if you were replacing a gear in your transmission... maybe not LOL.
DPittman
Ultra Member
Ya I won't be making any transmission gears anytime soon!
The tech details on the HMEM post kind of lost me, I'm not up to that speed yet (and not likely to ever be).
I ended up grinding the tool according to my gear I have and not the dfx image after all.
It sounds like the gears on this little engine have to be pretty close to right so I suspect I will have problems, but I gotta try!
DPittman
Ultra Member
So this is my attempt at broaching an internal bronze gear. To my ignorant eye it looks like it might work, but I will be surprised if it does in fact work for its intended purpose. I guess sometimes finding out what doesn't work is of almost equal value of finding out what DOES work.
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DPittman
Ultra Member
Yes, only problem with that is I think my internal gear is the one that needs the most wearing in and it's made of bronze while the better external gear is of softer brass. Do you suppose it would still be helpful?
Dabbler
ersatz engineer
if their hardnesses differ too much it doesn't work well at all. You can still polish the outer ring with toothpaste on a string or cloth to take the high spots off. It doesn't matter if your clearances are really large, say .001. I used to do this for brass crown/pinion gear sets and reduce the friction noticably, and made the linkage noticeably smoother.
DPittman
Ultra Member
Ok that will probably be worthwhile for me to do. I'm pretty sure the small gear would be significantly softer than the outer gear so the string method would be best. I'd eat my hat if I have tolerances as CLOSE as .001". My setup and methods leave " a bit" to be desired Lol.
Thanks for the advice.
Typically bronze is harder than brass, but depends on which alloy.
It might be useful to blue some teeth surfaces & get an idea where the wear is & how much. Sharpie marker works pretty good. You may find for example the rub is confined to a local area like crown radius in which case you might stand a better chance of dressing that feature. If its along the broached surface or say tighter in a one quadrant vs another, that would dictate a different remedy.
It might be useful to blue some teeth surfaces & get an idea where the wear is & how much. Sharpie marker works pretty good. You may find for example the rub is confined to a local area like crown radius in which case you might stand a better chance of dressing that feature. If its along the broached surface or say tighter in a one quadrant vs another, that would dictate a different remedy.
DPittman
Ultra Member
Well it is a 72 tooth gear and each tooth was supposed to have a .036" depth and I only cut about .001" max in a pass but I would estimate that I probably did at least 50 passes to get to that depth. Then after carving out 72 grooves I realized the ID of my gear had shrunk from spec due to the somewhat "forming" process of my broaching (think knurling). So with that in combination of tool deflection I decided my grooves/teeth were not deep enough. So I returned to broaching again for another .010" (min 20 strokes)
So I figure I made AT LEAST 5000 broaching strokes! Kinda crazy.
DPittman
Ultra Member
I don't suppose you have any ideas on how to identify which bronze alloy I have? I have a chunk that was bought from the scrap dealer as brass and when I picked it up to use last week I then realized it was bronze not brass. It turns beautifully on the lathe. It has the faint casting rings on the outside of the material. I'm guessing "bearing bronze".