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worm gear diameter
- Thread starter mce5802
- Start date
Thanks Terry! That's what I needed. I'm gonna get that book too. Sorry about the confusion with the new thread. Haven't had a chance to check back til now. I was planning to cut the gear with an acme tap and the gear mounted on a shaft in the compound of the lathe allowing it to turn. The tap should put the helix angle on the blank as it turns if my thinking is correct? Thanks a million. Lot of experienced help on this site, and it's appreciated.
You also are most welcome, Mike. Let us know how it goes. I am going to be sitting down with the book myself in just a bit since you fellas have my curiosity going now with the differences between spur gears and worm gears. Sorry I wasn't able to come up with the just the right numbers right off the bat, but that's how it goes sometimes in the hobby machining world.
Well, I'v at least learned that using a spiral flute tap is far preferable than using a straight flute. It's explained that when free hobbing a worm wheel, the space between the flutes will cause the wheel to stop and skip in its rotation. Makes sense to me and I have seen this happen first hand. That's why i have seen some videos where the operator has turned a concave into the wheel that is the same radius of the tap drill for that tap. Making this radius more than a 90* Arc allows the next cutting edge to enter the work before the last one leaves, provided your using a 4 flute tap.
Something around 135* seems to be working well for me.
Now I still need to find the math that works for this. I can cut the worm teeth but can't hit on the tooth count I'm shooting for. I have found this for inch threads , but it's not working for me -
- for the bottom of the grove. That just doesn't seem right to me, like it's missing something, and from mt results using it so far it would seem that my suspensions are correct. 
So I'm still looking for some good math on the subject and I'll post back if I stumble into anything useful.
Thanks everyone for your interest in this.
Mark
Something around 135* seems to be working well for me.
Now I still need to find the math that works for this. I can cut the worm teeth but can't hit on the tooth count I'm shooting for. I have found this for inch threads , but it's not working for me -
Code:
Number Of Teeth/TPI*PiSo I'm still looking for some good math on the subject and I'll post back if I stumble into anything useful.
Thanks everyone for your interest in this.
Mark
If you go to this link (WM BERG Gear Data) http://www.wmberg.com/tools/ and download the gear data you will get a calculation chart for alot of different gears,including worm gears, you input some data and it does the formula.
It's a pretty neat tool to use. I used it a lot when I was cutting the metric conversion gears for my southbend and they all worked out well
Good luck
John
It's a pretty neat tool to use. I used it a lot when I was cutting the metric conversion gears for my southbend and they all worked out well
Good luck
John
I done some reading on this a month or so ago. It seemed to me there was no hard and fast way to do the exact math. It really seemed to me that making the driven was a bit of trial and error.
Now I can tell you what I done... I found the tpi of the worm. Then went to the tap drill chart:nuts: and found a nut from the same tpi that best fit Dia of space I was filling. Then more or less flipped it inside out. The ID of the nut became the OD of the gear.
Two points
I was limited by size so all I cared about was the largest gear in that tpi that could fit in the space.
I learned the hard way that straight flutes stall the work. I have not got the spiral flute yet because it's a 24mm tap and not cheap. So I currently have no idea if my theory is full of idiocy or not ahaha
Now I can tell you what I done... I found the tpi of the worm. Then went to the tap drill chart:nuts: and found a nut from the same tpi that best fit Dia of space I was filling. Then more or less flipped it inside out. The ID of the nut became the OD of the gear.
Two points
I was limited by size so all I cared about was the largest gear in that tpi that could fit in the space.
I learned the hard way that straight flutes stall the work. I have not got the spiral flute yet because it's a 24mm tap and not cheap. So I currently have no idea if my theory is full of idiocy or not ahaha
Thank you Terry, I am going to give this math a try this evening. I have had a real miss and miss with this, hobbing a worm wheel with a tap. Was shooting for 40 tooth and first try ended up with 44 teeth. Second try after trying some other math, 36 and maybe 1/2 teeth.
What you have provided is completely different than anything else I have found on the subject. I'll now be shooting for a 36 tooth with a 1/2" - 13 worm.
If I did your math correct, I get a PD=0.8814 / DP=40.8441 / OD=0.9303.
Here's to hoping this time it works out.
One thing, how far will i want to advance the cutter (tap) into the work? Does 0.047 sound about right? (major diameter - minor diameter) / 2 or for a class 2A thread, (0.4985-0.4041)/2=0.0472
Again, thanks for your input on this.
Mark - (who is learning something new today)
I am a bit confused here. I assume that 1/2-13 worm translates to 13DP. I used e-machine software and I get different calculated numbers. My assumption is that 13 tpi does not translate to 13 DP, am I right?. Does anyone know how this translates?
Caster
EDIT: I referenced Ivan Law "Gears and Gear cutting" and got this formula for OD. OD = (N+2)/DP where N is the number of teeth and DP is the number of teeth per inch. So (36+2)/13 = 2.923. The TPI on the worm/screw is the DP and the OD should be 2.923 as e-machine computes.
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40 teeth would be for the pitch diameter. When you start you are operating at the OD which is larger and therefor has room for more teeth. I think you need to somehow cut some initial teeth to guide the hob (IIRC this is called gashing).
Suggestion: start with a tap with a slightly lower TPI such that 40 teeth will fit around the circumference. You might need to start with a slightly oversized blank . Use that tap to cut gashes well below the final OD. Then turn the blank down to final OD and finish with your "correct" tap, which should track the gashes.
Okay, I found a little more information on this, and I also redid all the math a little bit more carefully, first for Mike's 90 tooth gear using a 1 1/8-6 ACME tap, and then for Mark's 40 tooth gear using a 1/2-13 tap. Dimensions are all in inches unless noted otherwise. Here we go!
This method that I found for calculating worm wheels uses a constant in it's formula, and simplifies things quite a bit. There is one formula to calculate the OD of the gear blank, and another formula to calculate the face width of the worm wheel.
Number of teeth (N) of the worm wheel is determined by the desired gear ratio of 90:1. As we all know, with a single start worm, the number of teeth on the worm wheel is equal to the numerator of the gear ratio. In this case, 90.
Depth of tooth (D) needs to be known and we can get that information from Machinery's Handbook based on the tap that is being used to cut the worm wheel. In this case we are using an ACME tap, 1 1/8-6, which is .0933 for the total thread depth. Using the total thread depth should leave some clearance when operating which is a good thing.
Worm tooth Pitch (WP) which is equal to 1 inch divided by 6 TPI or 0.166666666
Face width (F) is calculated by the second formula.
.3183 and 2.38 are constants used in these two formulas.
OD = .3183 x WP x N +(2xD)
F = 2.38 x WP + 0.250
Here goes the math:
OD = .3183 x WP x N +(2xD) = .3183 x 0.166666666 x 90 + (2 x 0.0933) = 4.77449991 + 0.1866 = 4.96109991 rounded off: OD = 4.961"
F = 2.38 x WP + 0.250 = 2.38 x 0.166666666 + 0.250 = 0.646666665 rounded off: 0.647"
Mike needs a gear blank with an OD of 4.961" and a width of 0.647"
Now lets plug in the numbers for Mark's situation. He is using a 1/2-13 tap for cutting his worm wheel, and desires a 40:1 gear ratio.
N = 40
D = .0916 which is derived from .500 - .4084 (major diameter minus minor diameter) By using a class 3A thread dimension, we should have some clearance built in.
WP = 0.076923076 which is derived from 1" divided by 13 threads per inch.
OD = .3183 x WP x N +(2xD) = .3183 x 0.076923076 x 40 + (2 x 0.0916) = 0.9793846 + 0.1832 = 1.1625846 Rounded off: OD = 1.163
F = 2.38 x WP + 0.250 = 2.38 x 0.076923076 + 0.250 = 0.43307692 Rounded off: F = 0.433"
Mark needs a gear blank with an OD of 1.163" and a width of 0.433"
I almost forgot: Depth of cut can be figured very simply: Multiply the OD of the worm (not the worm wheel) by 0.2 and use this as the depth of cut. This will allow proper engagement of the teeth on each other to be able to transmit torque to the worm wheel without stripping any teeth, unless of course you get ham handed and really crank on it!
So there you have what I found. Mike and Mark, how do these numbers relate to the figures you guys were working from?? Let us know, as this is a great learning experience for all of us, me included!
This method that I found for calculating worm wheels uses a constant in it's formula, and simplifies things quite a bit. There is one formula to calculate the OD of the gear blank, and another formula to calculate the face width of the worm wheel.
Number of teeth (N) of the worm wheel is determined by the desired gear ratio of 90:1. As we all know, with a single start worm, the number of teeth on the worm wheel is equal to the numerator of the gear ratio. In this case, 90.
Depth of tooth (D) needs to be known and we can get that information from Machinery's Handbook based on the tap that is being used to cut the worm wheel. In this case we are using an ACME tap, 1 1/8-6, which is .0933 for the total thread depth. Using the total thread depth should leave some clearance when operating which is a good thing.
Worm tooth Pitch (WP) which is equal to 1 inch divided by 6 TPI or 0.166666666
Face width (F) is calculated by the second formula.
.3183 and 2.38 are constants used in these two formulas.
OD = .3183 x WP x N +(2xD)
F = 2.38 x WP + 0.250
Here goes the math:
OD = .3183 x WP x N +(2xD) = .3183 x 0.166666666 x 90 + (2 x 0.0933) = 4.77449991 + 0.1866 = 4.96109991 rounded off: OD = 4.961"
F = 2.38 x WP + 0.250 = 2.38 x 0.166666666 + 0.250 = 0.646666665 rounded off: 0.647"
Mike needs a gear blank with an OD of 4.961" and a width of 0.647"
Now lets plug in the numbers for Mark's situation. He is using a 1/2-13 tap for cutting his worm wheel, and desires a 40:1 gear ratio.
N = 40
D = .0916 which is derived from .500 - .4084 (major diameter minus minor diameter) By using a class 3A thread dimension, we should have some clearance built in.
WP = 0.076923076 which is derived from 1" divided by 13 threads per inch.
OD = .3183 x WP x N +(2xD) = .3183 x 0.076923076 x 40 + (2 x 0.0916) = 0.9793846 + 0.1832 = 1.1625846 Rounded off: OD = 1.163
F = 2.38 x WP + 0.250 = 2.38 x 0.076923076 + 0.250 = 0.43307692 Rounded off: F = 0.433"
Mark needs a gear blank with an OD of 1.163" and a width of 0.433"
I almost forgot: Depth of cut can be figured very simply: Multiply the OD of the worm (not the worm wheel) by 0.2 and use this as the depth of cut. This will allow proper engagement of the teeth on each other to be able to transmit torque to the worm wheel without stripping any teeth, unless of course you get ham handed and really crank on it!
So there you have what I found. Mike and Mark, how do these numbers relate to the figures you guys were working from?? Let us know, as this is a great learning experience for all of us, me included!