Breaking Plastic Gears??

[w6br]

What was your depth of cut. Remember brass trends to hog in which can cause issues.

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My depth of cut was approx. 0.010 or so, not very heavy at all and all was running smoothly. I was trying to get a smooth finish and was being careful??

Thank you,

Ron

 

[Baithog]

Brass should turn in the range of 200 to about 300 sf/min. That would put the spindle speed for 2", even with carbide, at 500 rpm. Brass also needs tool angles different than most off the shelf cutters. At that speed, and with a GP cutter, it wouldn't take a lot for the cutter to hog and strip some gear teeth. Also, running smooth is not necessarily running tight and smooth. The little lathes and mills are notoriously sloppy. Any lack of rigidity can muck things up right quickly. I had my 7X lathe for 5 years. I turned mostly steel under 1.5". I never lost a tooth. I know others that could strip a gear just by looking at it wrong. You may be one of them. But keep in mind that if those teeth didn't strip, then something else, something much more expensive, could have broken. Even the bigger bench lathes like the 10X22 have a plastic gear in the gear chain to sacrifice itself in the event of a crash.

 

[54hawken]

Brass should turn in the range of 200 to about 300 sf/min. That would put the spindle speed for 2", even with carbide, at 500 rpm. Brass also needs tool angles different than most off the shelf cutters. At that speed, and with a GP cutter, it wouldn't take a lot for the cutter to hog and strip some gear teeth. Also, running smooth is not necessarily running tight and smooth. The little lathes and mills are notoriously sloppy. Any lack of rigidity can muck things up right quickly. I had my 7X lathe for 5 years. I turned mostly steel under 1.5". I never lost a tooth. I know others that could strip a gear just by looking at it wrong. You may be one of them. But keep in mind that if those teeth didn't strip, then something else, something much more expensive, could have broken. Even the bigger bench lathes like the 10X22 have a plastic gear in the gear chain to sacrifice itself in the event of a crash.

When you said it happend on the third pass with your speed what it was I would guess your part probably gained .005 in diameter, thus increasing your depth of cut by approx. 50%.. Also if your insert was zero positive rake angle or chip breaker it tends to "suck" into part, and even more so when more pressure is applied due to diameter growth by heat. Using inserts with a negative rake angle should be used cutting brass. ( negative will appear to the eye like you are scrapping the metal off, positive will appear to your eye that it is cutting the metal off) If this fixes your problem on brass try steel same size stock using proper rake insert, proper feed and speed and reduce depth of cut 50%. I worked for Leblond as a field service technician for 10 years among other things I did for a living. Been retired a few years but still in my workshop machining several days a week at 71 Good Luck to you Don

 

[w6br]

Well Folks, Duh!!
I feel like a real Dummy!! I re-read all of the postings that were so greatfully replied to me and decided that there must be something amiss, so I tore back into the Lathe. Well I took the Carriage apart again, and took out the Split Nut, cleaned out all of the grease and guess what, some of the threads were buggered. Evidently, when it was molded some of the threads came out not formed and when the half-nut was threaded the threads didn't turn out so good. Eventually by using the Power Feed it worsened the threads and caused the Lead Screw and Split Nuts to bind shearing of the 80 tooth Plastic Gear!!
Now, in addition I am going to inspect the Lead Screw with a fine tooth comb!! I hope nothing else is bad. Anything else you Gentlemen suggest that I do.

Ok Grizzly here I come. I guess a number of your suggestion are correct in inspecting and THOROUGHLY cleaning the equipment before operation!! A word to the Wise!! Well, with diligence, WE finally found the problem and my heartfelt Thank You to you All.

That's what happens when you are a Newbie!! Thank God for this Site and all of your help!!

Merry Christmas,

Ron, w6br

 

[royesses]

Well Folks, Duh!!
I feel like a real Dummy!! I re-read all of the postings that were so greatfully replied to me and decided that there must be something amiss, so I tore back into the Lathe. Well I took the Carriage apart again, and took out the Split Nut, cleaned out all of the grease and guess what, some of the threads were buggered. Evidently, when it was molded some of the threads came out not formed and when the half-nut was threaded the threads didn't turn out so good. Eventually by using the Power Feed it worsened the threads and caused the Lead Screw and Split Nuts to bind shearing of the 80 tooth Plastic Gear!!
Now, in addition I am going to inspect the Lead Screw with a fine tooth comb!! I hope nothing else is bad. Anything else you Gentlemen suggest that I do.

Ok Grizzly here I come. I guess a number of your suggestion are correct in inspecting and THOROUGHLY cleaning the equipment before operation!! A word to the Wise!! Well, with diligence, WE finally found the problem and my heartfelt Thank You to you All.

That's what happens when you are a Newbie!! Thank God for this Site and all of your help!!

Merry Christmas,

Ron, w6br

Ron,
Thank you for letting us know what you found. Now to store that in the memory banks for future use. Check the alignment of those gears. Mine takes a .062" flat washer between the banjo and mount stud. Also I use hardened flat washers under the hold down nuts as the soft washers will deform when torqued and allow slip. The banjo moves around on these little machines and causes excessive backlash under load.
Merry Christmas and Happy Machining.
Roy