Shopsmith Forums

See post # 7.

Gene Howe wrote:OK, I'll answer.
No.

OKAY. What then is the most likely cause of a properly selected and properly secured set screw coming loose?

dusty wrote:OKAY. What then is the most likely cause of a properly selected and properly secured set screw coming loose?

Loose(sloppy) threads. Insufficient torque when tightening. Improper alignment of the arbor to the shaft.

But then you properly excluded two of those causes.


Sure that was a good idea?;)



I just have not experienced this problem. Yes at times the arbors come loose, but, I attribute that to improper alignment and tightening when it occurs. More careful exercise of same prevents recurrence.

Dusty,
Regarding set screws coming loose.....

Is it one specific arbor? Or possibly arbors for 1 1/4 rather than 5/8 ?

Why? Because one time I thought I remembered seeing a picture of a blade holder in your shop and each blade had a separate arbor. Just trying to narrow down the selection if possible. If it is one specific arbor then maybe it's tapped hole is worn out and time for SS to give you another or if it's all the standard or all the 5/8, then that might point to a common tapping problem versus a set screw problem.

Be well,
Ben

benush26 wrote:Dusty,
Regarding set screws coming loose.....

Is it one specific arbor? Or possibly arbors for 1 1/4 rather than 5/8 ?

Why? Because one time I thought I remembered seeing a picture of a blade holder in your shop and each blade had a separate arbor. Just trying to narrow down the selection if possible. If it is one specific arbor then maybe it's tapped hole is worn out and time for SS to give you another or if it's all the standard or all the 5/8, then that might point to a common tapping problem versus a set screw problem.

Be well,
Ben

Thank you for inquiring, Ben but I don't have a problem. Yes, I have several blades mounted on arbors. This makes blade change real convenient.

The initial post was intended to be a simple question.

If a longer set screw is used, does this increase the propensity for the set screw to work loose?

If it is an older arbor that has rust removed removed from the set screw and the arbor then enough metal may have been removed resulting in a sloppy fit.
More to the point, if the set srew has come from a inferior manufacturer such as one in a country whose name is similar to the kind of dishes my wife likes to use when we have company the threads may not have proper contact area to do the job properly.
As an example for a 5/16 X 18TPI set screw the hole could be drilled with a letter drill "G" for a 70-80% thread contact. This would be for cast steel, drop forged, or tool steel.
In most cases a 53% contact area will break the bolt before the threads strip. A 100% thread is only 5% stronger than a 75% thread but it takes three times the power to tap the hole
This information was taken from the "Machinist's Practical Guide" published by the Morse Twist Drill & Machine Co. and was copyrighted in 1950 but I don't think these specs have changed much.
Bill V
PS. I don't think the length of the set screw will have an effect but the precision that the threads have been machined to probably will. If the pitch of the threads on the screw are a poor match to the threads in the hole all bets are off. Bestsolution is to put a small drop of RTV on the threads and it will act as a thread locker and still permit the set screw to be removed easily.

wa2crk wrote:If it is an older arbor that has rust removed removed from the set screw and the arbor then enough metal may have been removed resulting in a sloppy fit.
More to the point, if the set srew has come from a inferior manufacturer such as one in a country whose name is similar to the kind of dishes my wife likes to use when we have company the threads may not have proper contact area to do the job properly.
As an example for a 5/16 X 18TPI set screw the hole could be drilled with a letter drill "G" for a 70-80% thread contact. This would be for cast steel, drop forged, or tool steel.
In most cases a 53% contact area will break the bolt before the threads strip. A 100% thread is only 5% stronger than a 75% thread but it takes three times the power to tap the hole
This information was taken from the "Machinist's Practical Guide" published by the Morse Twist Drill & Machine Co. and was copyrighted in 1950 but I don't think these specs have changed much.
Bill V
PS. I don't think the length of the set screw will have an effect but the precision that the threads have been machined to probably will. If the pitch of the threads on the screw are a poor match to the threads in the hole all bets are off. Bestsolution is to put a small drop of RTV on the threads and it will act as a thread locker and still permit the set screw to be removed easily.

A lot of good information here. Thanks for the response.

A am going to try to find that reference document and do some more reading.

BTW I have gotten all of my set screws from either Fastenal or from Shopsmith. Knowing that I have very little concern that they might have come from China or any other questionable source.

Dusty
I don't think that you will be able to find the reference that I quoted. It is a small notebook that my Grandfather gave me shortly after he retired and I was working a summer job in a manufacturing facility. There is no Library of Congress info and it is about 3" by 5" so that someone could carry it in a shirt pocket.
Bill V

wa2crk wrote:Dusty
I don't think that you will be able to find the reference that I quoted. It is a small notebook that my Grandfather gave me shortly after he retired and I was working a summer job in a manufacturing facility. There is no Library of Congress info and it is about 3" by 5" so that someone could carry it in a shirt pocket.
Bill V

Well lookie here ... right now there is one for ten bucks if you hurry