Michael G
31st January 2015, 02:35 PM
I think one of my faults is I think too much, followed usually by not thinking enough.
The thinking too much bit usually starts with "Hmm. How would I do that?", followed after a while with "But would that work?" and then "I'd better try it before I suggest it".
The questions I don’t ask (the not thinking enough part) are along the lines of "Yes, but if I make one, what will I do with it" and "I could probably make one but would it be better to let X gain the experience/ satisfaction/ have the pleasure" and so on. (My wife would probably add "how much will it cost", but let's not go there)
This story is probably triggered by Andre and his Stent story. In order to make it work he needs a rack and pinion. A pinion is not an issue. I've made lots of spur gears and I'd like to think I have a pretty fair idea on how to make them. The rack was another matter. I did some small racks for Bob recently but they were a bit of a cheat – at only 50mm long or there about, not a great stretch at all. I am meaning to (one day) make up a rack cutting head and index mechanism for the mill but time, money and other considerations mean that it has not happened yet.
(The "how would I do that" thought)
Andre needs a 20DP rack, 3/8" square and 9" long. No. can't do it. No way of getting a cutter rotating parallel with the long axis of the mill. Although… The horizontal arbor is around 13" from bearing to drive flange…theoretically the cutter could be moved in say 3 or 4 inch increments along the arbor if the rack blank was perpendicular to the long axis. Well – that might work. Still, I couldn't do it as I have no way of holding the blank. 3/8" isn't much to hold onto, especially with a 2.74mm DOC – could I start with something deeper, cut it off later. Yeah, that could work. Still got to hold it on the mill table though. Turn the vice around? No. I'd have to remove the key on the bottom, lining it up and then holding it would be a pain and I couldn't get a good swing on the handle to tighten it. Just as well. I've got enough to do at the moment. Really needs something like some toe clamps... Hang on – I think I have some of those in a drawer that I got once for a low profile job. Probably just fit too. Hmm.
(The "but would that work" thought)
So – hold a deeper than needed blank with some toe clamps, cut with a rack cutter and move the cutter along the arbor as needed, indexing the circular pitch to cut the rack. Yes, potentially that might work.
(And then)
I suppose there might be some issues I haven't thought about. Better try it I guess. Wouldn't want to suggest something that isn't terribly practical…
and so, Alea iacta est ("The die is cast"- attributed to Julius Caesar)
It turned out the job was relatively easy. I clamped the blank upright between some strips of material so I had cutter clearance , In the foreground you can see the toe clamp - this is a commercial one called 'Mitee-bite" but Harold Hall (who signed up recently as a member) I recall did a "how to make" in MEW several years back. For clamping of low profile jobs they are very good.
338687
The next photo is about half way through. At just under the 3" mark I would stop, wind the table back and then reposition the cutter on the arbor. Line the cutter up with a cut, index and off I'd go again. This rack took 4 changes but surprisingly they did not take long and realigning the cutter was easy.
338686
The final result - I made up a test gear to try on it - it meshes nicely. There do not seem to be any awkward or hard spots where I repositioned so I guess I can say that yes, this is one way to make a short length of rack.
338685
Of course, now I have an ethical dilemma - (One of the things I didn't think about in the first place). Do I give this to Andre and prevent him having the learning experience of doing it himself, or should I keep it - even though I have no use for it - so he can gain that experience?
Michael
The thinking too much bit usually starts with "Hmm. How would I do that?", followed after a while with "But would that work?" and then "I'd better try it before I suggest it".
The questions I don’t ask (the not thinking enough part) are along the lines of "Yes, but if I make one, what will I do with it" and "I could probably make one but would it be better to let X gain the experience/ satisfaction/ have the pleasure" and so on. (My wife would probably add "how much will it cost", but let's not go there)
This story is probably triggered by Andre and his Stent story. In order to make it work he needs a rack and pinion. A pinion is not an issue. I've made lots of spur gears and I'd like to think I have a pretty fair idea on how to make them. The rack was another matter. I did some small racks for Bob recently but they were a bit of a cheat – at only 50mm long or there about, not a great stretch at all. I am meaning to (one day) make up a rack cutting head and index mechanism for the mill but time, money and other considerations mean that it has not happened yet.
(The "how would I do that" thought)
Andre needs a 20DP rack, 3/8" square and 9" long. No. can't do it. No way of getting a cutter rotating parallel with the long axis of the mill. Although… The horizontal arbor is around 13" from bearing to drive flange…theoretically the cutter could be moved in say 3 or 4 inch increments along the arbor if the rack blank was perpendicular to the long axis. Well – that might work. Still, I couldn't do it as I have no way of holding the blank. 3/8" isn't much to hold onto, especially with a 2.74mm DOC – could I start with something deeper, cut it off later. Yeah, that could work. Still got to hold it on the mill table though. Turn the vice around? No. I'd have to remove the key on the bottom, lining it up and then holding it would be a pain and I couldn't get a good swing on the handle to tighten it. Just as well. I've got enough to do at the moment. Really needs something like some toe clamps... Hang on – I think I have some of those in a drawer that I got once for a low profile job. Probably just fit too. Hmm.
(The "but would that work" thought)
So – hold a deeper than needed blank with some toe clamps, cut with a rack cutter and move the cutter along the arbor as needed, indexing the circular pitch to cut the rack. Yes, potentially that might work.
(And then)
I suppose there might be some issues I haven't thought about. Better try it I guess. Wouldn't want to suggest something that isn't terribly practical…
and so, Alea iacta est ("The die is cast"- attributed to Julius Caesar)
It turned out the job was relatively easy. I clamped the blank upright between some strips of material so I had cutter clearance , In the foreground you can see the toe clamp - this is a commercial one called 'Mitee-bite" but Harold Hall (who signed up recently as a member) I recall did a "how to make" in MEW several years back. For clamping of low profile jobs they are very good.
338687
The next photo is about half way through. At just under the 3" mark I would stop, wind the table back and then reposition the cutter on the arbor. Line the cutter up with a cut, index and off I'd go again. This rack took 4 changes but surprisingly they did not take long and realigning the cutter was easy.
338686
The final result - I made up a test gear to try on it - it meshes nicely. There do not seem to be any awkward or hard spots where I repositioned so I guess I can say that yes, this is one way to make a short length of rack.
338685
Of course, now I have an ethical dilemma - (One of the things I didn't think about in the first place). Do I give this to Andre and prevent him having the learning experience of doing it himself, or should I keep it - even though I have no use for it - so he can gain that experience?
Michael