Angular groove in round tube

[francist]

Thought about doing it by eye, but the taper needs to be smooth. No dips or flat spots.

I’m sitting here twiddling one of my old Millers Falls screwdrivers…. If I hold the usual “blade” end of the driver solid in my hand, the barrel which is attached to handle needs to follow that helical groove in the shaft as I turn it. If I were to fix a tube of metal to the front of that barrel part and turned it, it too would follow the proscribed helix.

Could you use this to advantage and somehow fix your part to be cut to the barrel of the screwdriver so that now your part travels the desired helix? If the blade end of the driver is secured in the stationary lathe chuck with the handle supported at the tailstock, would you be able to rotate the barrel/part past the pencil grinder in your tool post in a smooth and controlled enough manner to cut your groove? Just spit balling…

-frank

 

[RJSakowski]

With a rotary table and the mill,you can do fairly accurate representation of CNC with a fourth axis. You won't need to twist the rt. Just increment the rt and the mill axis parallel to rt axis to cut the helix. The smaller the increment, the more accurate the cut. My impact driver has the helix cut with a ball end mill and two ball bearings.

 

[Chewy]

Some good ideas. Let me try to think about them. On the DRO, what procedure do you use to plot the increments? I don't that much with the DRO. PCD and absolute and increment and stored settings. I read somewhere there is a procedure to plot curves, but don't have a clue as to what it is.

 

[Eddyde]

My DRO has a function for plotting curves. Once you enter the parameters, you move each axis till it reads X 0.000, Y 0.000 then hit enter, it then displays the offsets and you move to zero-zero again, repeat till done. However in this case, you wouldn't be able to use the DRO as you won't have an encoder on the rotary table, so you'll just have to do it manually. For example, If the length of your finished cut is say .5" and you divide it by .01" you will have 50 increments, but you'll also have to add the diameter of the tool, say it's .125" so you will have to move 63 increments on the X axis. Do the same for the rotary axis A. Figure the total degrees of rotation you want on your finished cut (sans tool allowance), say 40° divide that by the increments of the finished cut, 50 = .8° So at each increment you move the X axis .01" and turn the A axis .8°
I hope that makes sense.

 

[Mill Lee farm]

Just trying to understand your intent. Doesn't a small impact driver (I have a Milwakee M12 that is great) perform this task for you? Are you wanting to do this by hand by just 'pushing'? Are you planning on tapping it with a small hammer etc?
I think it's an interesting excercise, I'm just not following the usage case. (but I'm probably just too dumb!)

 

[RJSakowski]

I would decide how much axial advance I wanted per degree of rotation and make my increments accordingly. e.g., if I want to advance 1/2" in 1/4 turn, it would be 90/.500 or .18deg/.001".

 

[Chewy]

To all the above. This is a .075 diameter rod about 1 inch long. It is a pivot for a key on a clarinet. The top and bottom posts are in the clear..It is a plastic body so the post can't be unscrewed and removed. I intend to work a shim in between the key and the post to remove any clearance. I have a small tab sticking out with a .250 ball recess in it, made with a ball end mill. I am going to hold the clarinet body upright. I am going to press down and rotate by hand enough to apply some pressure and then rap it with a hammer. I only need shock to break it loose. Degrees of rotation is a non issue. Once it moves at all, I can turn it with a screwdriver. I turned it hard enough to twist the blade end of the screwdriver, so I learned how to make replacement blades. Yes you can buy them at $21 a piece or make a bunch of them for $3. Making them and re-tipping them keeps the wife happy.

Soaking with Kroil and several others didn't work. You really can't heat it because the plastic body starts to melt. Other option is to cut the key loose and then drill and tap it. In this case that will be difficult because of the key location.

I have another where the thread end goes into the side of the body. In that case the outside post could be unscrewed and the thread end drilled out. It seems that replacement rods are A1 or O1 steel, not hardened. I have the rod and dies to make the replacement pivot rods. And several current repair books say to use Locktite when putting screws back together which is probably the case here. That way the instrument can be repaired once and then thrown away. I mean everything else today is disposable.

I have a box of broken clarinet parts from Ebay. You know, a dozen broken bodies for $10. I am working on ways to salvage them. Making repair jigs, making parts, etc. The one I can't drill is one of them The one I can is a real one, worth about $4-500 if repaired.