Helix angle calculation – thread dial

[Perk]

Can someone post the calculation for thread helix angles? I need to make a thread dial for a Stanley Engine, the Major Dia. on the screw is 2.25 with 2 TPI. If my figures are right the pitch Dia. is 2”. I didn’t get any manuals with this machine so if someone could help me out here, that too would be appreciated. Stanley 1704 made in Halifax England.

 

[dsergison]

being a zero load appication it doesn't really matter.

and far easier to tell you that than to figure it out.

 

[johnoder]

If 2" P.D.:

(2.000 X 3.14159) divided into .500" = 0.07958 = tan of 4.55 degrees.

John

 

[lathefan]

If you don't mind having a canted threading dial, make a mount for it that allows you to tilt it to line the teeth up with the leadscrew.

 

[Perk]

I don’t have a problem with a canted or tilted thread dial but I didn’t think it would be a problem to apply the helix angle to the teeth on the spur gear either. My experience with gears is fairly limited, machined a few straight tooth spur gears on horizontals but that’s about it. What am I over looking?

 

[carlquib]

I have made several of these threading dials. All I did was to fixture the blank at the appropriate angle, I measured mine to get a good enough approximation, then ground a single point tool that matched the thread profile. Then it was just a matter of turning the crank on the dividing head and gashing out the teeth. Not very pretty but very functional and takes less time than making a hob.

-brian

 

[EPAIII]

Acme thread is very symetrical. Measure the OD or Major Diameter. Measure the Minor Diameter. Add them together and divide by two for the pitch diameter. Multiply pitch diameter by pi (3.141) to get the circumference at the pitch diameter. Divide the lead (1/TPI if Engilish) by the pitch circumference and take the arc tangent of that value to find the helix angle.

Overall formula:

HA = arctan(L/((OD+MD)*3.141/2))

HA is Helix Angle
L is Lead
OD is Outside Diameter
MD is Minor Diameter

Be sure all measurements are in the same units.

Paul A.

 

[Lumpsmith]

The gear on my Emco Maier V-13 is thin, about 1/16" thick so helix angle does'nt matter.If your lathe lead screw does'nt have a slot in it for power feed you can make your gear the same.