Thread: custom lathe tool

Originally Posted by astjp2

I do have radius gauges and precision protractors, I was just trying to make this a simple process to build several pulleys at a time, there are 2 pulleys in the system. The other pulley has a broach cut out of the center hole also. I am trying to sustain a fleet that is on average of 78 years old. The cable is 1/16, if the radius is too small, it will split the pulley, if it is too large, it will slip. I have a bunch of tooling and fixtures I need to make over the next few years. It is a frustrating process, having to learn as I go. I do appreciate everyone's comments, I am still hoping that someone can tell me who can grind me a tool that can make the groove in this pulley. I am thinking that I may have to make a .050 wide square tool for the first cut, then one that meets the above profile for the second one. Would that work? Regards, Tim

I think Sami was offering to grind it for you for $150.

You could do what is essentially a parting cut using a .050 square-ended tool ... but keep in mind tha your tolerances call for the diameter at the bottom to be .030-.050. Especially for a newbie with "not much of a lathe" to work with, awfully likely that you'd wind up with something larger than .050 if that is the size of your tool.

Why not make a tool .040 wide and put a radius on it. Your tolerances are such that it does not appear that a perfect radius is required, so long as the overall width stays within .030-.050. Rather than a form tool to cut the angled sides, just set the compound to cut the angles and make two passes.

I used to make form cutting tools. I think a full form would not work in any kind of plastic. There is just too much area to cut so even a .001 in-feed would be to much stock to cut. Plus you would need positive rake all around the cutter..
Going to depth with a parting tool , and then cutting the two 15* sides one at a time with the likes of a single point tool bit may be the best way to go. Yes the compound at 15* this way and then at 15* the other way so you might shave .015 or so per pass.

Parting tool .050 could have the .025 radius

Figure 3/16 on one side and 3/16 on the other side and .050 that is almost 1/2 inch of in-the-cut x .001 of in-feed is more that many machines will cut.

would this work for me if I get the tip radiused?
45621 Solid Carbide 30 Degree Engraving 0.035 Tip Width x 1/4 Inch Shank Signmaking

the radius is for stress relieving to prevent cracks, the cable only rides on it, like the elevator sheaves the traction is from side load and flex/lack of flex of pulley/cable (same as v belts, morse taper tools, ect.). a .0625 cable will not sit in a .04 hemisphere, it sits on a .04 hemisphere.

I think that a parting tool is the way to go, now I need to get this tool radiused and profiled.

I think a few here are having a problem reading the numbers on that dwg. :-)
...lewie...

Originally Posted by astjp2

would this work for me if I get the tip radiused?
45621 Solid Carbide 30 Degree Engraving 0.035 Tip Width x 1/4 Inch Shank Signmaking

As I read your drawing, you need 15° total angle, not 30°.

Yeah, I discovered that after I posted the link. Local tool grinder quoted me $67 to build me one and he is supplying the cutter. Now I need to make a mandrel to put in my 5c closer.

This is kinda like a pulley grooving tool.... oh wait it is a pulley groover just not steel being cut so different clearance and rake.
Just curious is the $67 carbide or HSS? Top hook or other? This material likes very high shear plane angles.
Thats a real decent deal as my setups would eat that price tag for lunch and still be hungry.
Bob

just a thought and coudl be totaly wrong what if he had the parting tool and then a left and right side tool ground that way with a QCTP you could swap them out faster then adjusting the whole tool pos for left and right side cuts

Originally Posted by CarbideBob

Not sure I understand the serious question.
Fairly wide open tolerances although I do hate one sided rad callouts as you don't know where the best zero really is.
With it so open here I'd make halfway inside which might not be the best choice. (Actually I'd usually contact the customer and ask)

When I get stuff like this I almost always redraw it, for the radius I draw the two side angles hitting a flat root at the bottom of the intended radius. Then a circle tangent to the sides and root. 99/100 (or more) it's "perfect" as the radius there is just a clearance anyway. If it's a functional radius and customer sent a dumb drawing then yes a call is in order. Doesn't always clear things up but it'll CYO a little at least!

For something like this pulley I'd probably chop out a simple brass gage and 3 HSS tools for sides and root. Easier to measure the male part.

Originally Posted by CarbideBob

This is kinda like a pulley grooving tool.... oh wait it is a pulley groover just not steel being cut so different clearance and rake.
Just curious is the $67 carbide or HSS? Top hook or other? This material likes very high shear plane angles.
Thats a real decent deal as my setups would eat that price tag for lunch and still be hungry.
Bob

I would assume it is HSS. I wish I had a picture to see so I can get it in my mind how the cutter is supposed to be set up to cut phenolic. I just looked at 2 of the pulleys that I bought from someone, they just used a threading tool to cut the groove. Not to spec and I think the cable will slip in short order. What about using a custom ground threading tool that will fit my BXA tool holder vs. the parting tool holder.?

I know that this is an old thread, I wound up getting a glass impregnated phenolic and it may be tougher to cut than I expected. There is a local machinist who says that he is willing to try to make the pulleys, I still really need to decide if I make a .040 wide radius straight tool and then a finish cut with the 15 degree tool or if I can just cut it with the 15 tool.

Qt ; [I still really need to decide if I make a .040 wide radius straight tool and then a finish cut with the 15 degree tool or if I can just cut it with the 15 tool.]

You might make/grind a parting blade to the width and radius..easy on a bench grinder.
And then come in on each side to single-point using the compound for 15* right and then left angle to intersect the radius.
If needing only a few pulleys this may be best/Ok.