Thread: 14.5 degree Pressure Angle full sized teeth sheet

I find the problem with these online sheets, that they are never to scale once you print them out...

A quick google found this informative thread started by PeteF.

http://www.practicalmachinist.com/vb...r-s-pa-203860/

Hi Bob,
We have been discussing this a fair bit on the Holbrook yahoo group. At some stage during the C10's manufacturing they went to 20PA gears. But they did not do all the machines gears all at once.....

My C10 is 67yo but has 20PA change gears, so it may be possible your drill has 20PA gears despite its age. If you hold 2 of the same size gears side by side, one 14.5 and one 20pa it is plain to see the difference. If they look like 20 with a cast then they will be. Compare it to the 14.5pa that you have posted and you should be able to tell.

Ew

Attached is a scan from a 1927 machinery's handbook that should be 14 1/2 degrees (it talks of these as "standard gears" and the new 20 degree pressure angle gears used in automobiles)
gear size.jpg

The ruler on the LHS is so you can get an idea of scale.

Michael

You can buy gear pitch gauges (like thread gauges but for gears) and they come in 14.5 and 20 degree PA sets as well as metric sizes. They are real handy to quickly find out what DP and PA you are dealing with.

Thanks to all for the response,this is what makes this a great forum.
RC,
I agree that the print outs are not real accurate but they do narrow down the options. I have had a quick read of the link you provided it contains a lot of information, I will have to spend some time reading it again to absorb it.
Ueee,
Interesting information on the swap over time on your C10 Holbrook. Despite a fair bit of searching I have not been able to narrow the build date down on this drill, somewhere between 1920 to late into the 30's. I will have to pull a few other gears off the drill and see if they match the spindle rack. The resin casting I took looks like a 10 DP 20 degree PA as best as I can judge from the printed sheet. If Hurcus had a similar shet for 14.5 degree gears it would have made a comparison a lot easier.
michael G,
Thanks for the scan from the 1927 MH. It is hard to make a decision from just pictures, you can see the different profiles clearly but looking at an old worn gear and the pictures is a bit more difficult.
markgray,
The gear gauges sure would be a handy tool to have and would make a true comparison easy. I have only ever seen one second hand set for sale and they were way overpriced.I will make a few telephone calls to some local engineering shops to see if any of them have a set.
Bob

Plan B. Get a strip of plasticene, put it on a flat surface and then roll a gear along (that is, produce a rack). The teeth should have an angle of either 20 degrees or 14.5 degrees. (I won't say which is which)

Michael

Can you give the DP of any of the gears you have and a tooth count of the same gear you are measuring.

With this information a calculation can be made.

Originally Posted by pipeclay

With this information a calculation can be made.

Not according to any online resource I have found..


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Seems to be a number of online graphical gear generators... I would use one of them to print out a 14.5 and a 20 gear and use that as a template.. It seems to be the easiest solution..

For example https://woodgears.ca/gear_cutting/template.html

Michael G and pipeclay,
Thanks for your reply's.
michael g
A good suggestion but I do not have an intact gear to roll out,the rack half teeth are OK,the pinion teeth are rather second hand as you can see in the pictures.
pipeclay,
I used the formula of DP= number of teeth +2 divided by the outside diameter of the gear and came up with a DP of 9.25,does this make sense? The od of the shaft is 1.620" and it has 13 teeth.
Bob

Plan C. Step back and use a camera to zoom in onto the rack*. Take a picture of the rack profile and use a protractor/ geoliner to measure the rack tooth angles. My rough and ready measurement on the screen suggests 29 degrees - PA = 14.5 degrees.

Michael

*(You want to be as far back as you can while still getting a decent picture to avoid distortion)

Your calc for DP is not correct.

It should be number of teeth divided by OD.

I think it should be 8 DP i worked on 1.625" OD.

If you can find two good teeth next to each other measure the distance between them.

If you come up with a figure of .579" it should be 14 1/2 PA.

If you come up with .576" it would be 20 PA.

There is not a lot of variation between the 2 sizes and the amount of wear could/will effect your measurement.

You may be able to do this check over the rack if its not to badly worn and come up with a similar figure to the ones above.

At the end of the day seeing this is only being used manually I dont think it would matter greatly as to what PA you use as long as the DP of both are the same.

If it was in a mechanical situation you may find that gear noise would increase if using different PA's.

Originally Posted by krisfarm

I used the formula of DP= number of teeth +2 divided by the outside diameter of the gear and came up with a DP of 9.25,does this make sense? The od of the shaft is 1.620" and it has 13 teeth.

That doesn't make sense but I think that is because you used the OD of the shaft and it looks like it was stepped. I've scaled the gear diameter from your photos and get a gear OD of 1.5", which using the formula DP=(n+2)/OD gives a DP of 10. I think this is more likely. If you measured the teeth on the rack a 10DP rack should have a tooth pitch of 0.314"

Michael

pipeclay and Michael G,
Thanks both of you for the further input.
pipeclay.
I meausured the OD of the shaft on the plain section not over the gears as they are too worn and it measures 1.620" which is very close to your 1.625". I have found two different formulas for working out the DP, very confusing for a novice gear cutter.
Michael G.
The stepped look on the pinion gear is caused by wear/abuse as this drill at some time in its life has been left running with the down feed engaged and the manual handle left in the engaged mode which has resulted in a heavy crash that has sheared both sets of the handles dog gears.Yesterday I measured the pitch over the top of two of the best looking gears on the rack and came up with 0.310" which is very close to your 0.314". Earlier today I took both gears for a car ride into an engineering shop that I have dealt with for a lot of years and they cut a lot of gears. After a few minutes checking cutters both 14.5 and 20 degree PA we found that a 10 DP 20 Degree PA cutter was the closest match.
Bob