LT70 Main Drive shaft sheared

just_sawing · September 20, 2013, 11:05:52 AM

Just had an unexpected failure on my LT70.
The Drive for the DC shft sheared. Theyhad them in stock so I should be back up toshearing a shaft isn't what I expect to see. Oh well at least I have a brak to play machinest.

moosehunter · September 20, 2013, 11:21:25 AM

Looks like it has been in service for awhile! How many hour on your mill?

drobertson · September 20, 2013, 05:22:45 PM

Hard to believe the breaker did not go before a seize up? david

just_sawing · September 20, 2013, 06:38:07 PM

2600 hours is all
The shaft never seized. If you look at the part there is little or no radius from the smaller shaft to the larger. That is a stress riser in other words design fault. I have replace shafts for companies before with the same problem. It is hard to fathom that a sharp corner can cause thing to break.

beenthere · September 20, 2013, 07:03:27 PM

"Sharp corner stress concentration" is a problem as shown and illustrated in this report.
http://www.ewp.rpi.edu/hartford/~ernesto/Su2012/EP/MaterialsforStudents/Aiello/Roark-Ch06.pdf

drobertson · September 20, 2013, 09:22:05 PM

It has to be a defective shaft, I ran an 06' 70 for 20 hrs, dragging 7x9's at full speed last winter, no issues, this particular mill had twice the hours on it, david

Bill Gaiche · September 20, 2013, 09:57:31 PM

A little break never hurts. Did you do the Lebanon fair this year? bg

just_sawing · September 20, 2013, 10:06:05 PM

Had a great time with a lot of sawdust made.
They had 583,000 people. It is a hard eight days but it is a family reunion of old friends

pineywoods · September 21, 2013, 09:36:19 AM

I have seen that shaft fail on LT40's Usually the bearing seizes and turns on the shaft. The resulting heat weakens the metal There's a lot of stress on that shaft. Have one in my shop awaiting repair, weld and grind down true.

just_sawing · September 21, 2013, 12:50:32 PM

The 70 has two bearing to support with a Double Chain coupling which is good. I cut cross ties and pushing them back got it. That is the only thing except for there not being a good radius on the shaft.

Chuck White · September 21, 2013, 03:24:30 PM

I don't know much about the LT-70's, so.... What does this shaft do?

Just picking up bits and pieces in the posts, it sounds like it is in the sawhead feed system.

just_sawing · September 21, 2013, 03:46:58 PM

This is the coupling shaft connecting the DC gear box to the Chain sprocket. The Chain sprocket gear sheared off about a 1" shaft. It appears that where the shaft goes from a 1" TO A 2" shaft the radius is cut too sharp which causes a stress riser.

Chuck White · September 21, 2013, 04:10:01 PM

I guess the difference between an LT-40 and LT-70 is greater than I thought! :-\

customsawyer · September 21, 2013, 05:12:34 PM

I have almost 9000 hours on my mill and most of it dragging back 40 ft boards. Never had this happen but I guess I will watch out for it.

Bill Gaiche · September 21, 2013, 06:27:33 PM

Good turn out. Thats one nice fair they have. Would like to do it again sometime. bg

just_sawing · September 21, 2013, 07:54:43 PM

One thing anything mechanical will break. But it is nice that 23 hours after I ordered a part it was on my back poach. That makes the difference when dealing with a great company.

backwoods sawyer · September 22, 2013, 09:10:31 PM

Quote from: just_sawing on September 21, 2013, 07:54:43 PM
One thing anything mechanical will break. But it is nice that 23 hours after I ordered a part it was on my back poach. That makes the difference when dealing with a great company.

Down time is inevitable, minimising it and getting back into prodution is the key.
easing into the piece being drug back will take some of the shock out of the chain as will keeping the chain at the correct tention so as not to have to much slack may help a bit as well.