Shopsmith Forums

Mike,

if you are serious about finding out the failure mode, then do NOT try to clean up the fracture surfaces until it is time for the repair.

in your pictures, it looks like the upper part of the fracture on both sides is a little brownish. if the mating surfaces have a similar (matching) color pattern then you may have had a pair of cracks slowly propagate across the part.

if there is not a matching color, then the hoop may have just been laying in something.

unfortunately, the guy that taught me fracture mechanics (and was a good forensic metallurgist) has retired. that part of mechanical metallurgy was not my strong point and the class mostly did steel fracture.
there had been a high pressure bottle-field failure not long before the class and the prof made sure that we understood that as-found fracture surfaces were critical for analysis. some of the pieces from the bottle-field got wire-brushed to clean them up before he got to see them. to this day, I am glad that I was not one of the techs who did that.

Ivan

This thread is going to get very interesting.

I would have looked at all of this and simply concluded that the jig saw was dropped - point of impact was the dent - result was the fracture - end of analysis.

Yep... Its broke.
I would cheat on that one. My closet neighbor repairs racing boat props for a living... He also designs custom props. He worked for a prop company for years but now makes 5 times what I ever did working out of a shop in his back yard. He is a whiz at such repairs and has done a number of jobs for me like filling in sections of aluminum engine blocks etc. I try to not take too much to him because he won't charge me and I want to treat him right. Something like that broken ring though I would probably take to him. If he did that much work on a prop he would probably charge around $300+. Stays buried in work...
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A lot depends on whether you are "restoring" or "making it work". I see several easy repairs that will "make it work" but they are not "restoring".
The simplest would be to clamp the end of the saw body down to the quill with something like a "U" bolt clamp or one of several types of clamps. Even a very large screw type hose clamp or two would be "MUCH" stronger than JB Weld. I have used JB Weld for many years and it is a good product but it is easy to over expect from it... It is fine as a filler and a "little" for structural strength but it is not suitable for critical holding just like you shouldn't pass a huge bowl of hot gravy down the table being held together with model cement.
I would have to look closer but one type of repair I would consider would be to find (or make) a thick washer/ring to fit up against the housing and with the proper size hole to fit the quill. I would then drill a number of small holes around it and drill and tap matching holes in the housing and the broken piece. Then I would maybe attach the washer/ring with a series of small machine screws with an application of JB Weld between the cleaned housing and the washer/ring. Not perfectly original but a good viable repair that if painted over could look like it belonged.

Mike,

As usual I have comments, but unfortunately not much time tonight. I will try later...

In the mean time you and Dusty can enjoy the link to the pamphlet I posted.

When you guys tackle that I will post the link to the serious reference.

Troy

dusty wrote:This thread is going to get very interesting.

I would have looked at all of this and simply concluded that the jig saw was dropped - point of impact was the dent - result was the fracture - end of analysis.

You must be wondering why the heck we're going through all this brain twist. You may just be right dusty. It could be the dent that caused it all. The dent was an unknown until I was taking the photos. That's when I noticed it. But.....it could be that the dent isn't what caused it to break at all....Reminds me of this story.....

Evidence:
One man drinks whiskey and soda. Result: Man gets drunk
Another man drinks gin and soda. Result: Man gets drunk
A third man drinks scotch and soda. Result: Man gets drunk

Conclusion:
If you know nothing about alcohol, you'd conclude the since the thing in common with the three men getting drunck was "soda", it must be the soda that makes you drunk.

Kind of a corny story but for whatever reason, it had stuck with me throughout my life. It came from a college professor who would always stressed that unless you know for sure why something happens, your knowledge is, as he put it "meager, to say the least".

My dad (the cop) used to constantly say...."Things aren't always as they seem". That stuck with me too.

I like trying to get a better understanding of what causes it to break (the engineer in me). That can lead to select the best method of repair.

horologist wrote:Mike,

As usual I have comments, but unfortunately not much time tonight. I will try later...

In the mean time you and Dusty can enjoy the link to the pamphlet I posted.

When you guys tackle that I will post the link to the serious reference.

Troy

Went through that quick reference guide you posted. Found a couple errors in it. Got anything a little more meaty?

robinson46176 wrote:Yep... Its broke.
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A lot depends on whether you are "restoring" or "making it work". I see several easy repairs that will "make it work" but they are not "restoring".
The simplest would be to clamp the end of the saw body down to the quill with something like a "U" bolt clamp or one of several types of clamps. Even a very large screw type hose clamp or two would be "MUCH" stronger than JB Weld. I have used JB Weld for many years and it is a good product but it is easy to over expect from it... It is fine as a filler and a "little" for structural strength but it is not suitable for critical holding just like you shouldn't pass a huge bowl of hot gravy down the table being held together with model cement.
I would have to look closer but one type of repair I would consider would be to find (or make) a thick washer/ring to fit up against the housing and with the proper size hole to fit the quill. I would then drill a number of small holes around it and drill and tap matching holes in the housing and the broken piece. Then I would maybe attach the washer/ring with a series of small machine screws with an application of JB Weld between the cleaned housing and the washer/ring. Not perfectly original but a good viable repair that if painted over could look like it belonged.

You sure have some interesting "make it work" fixes there farmer. I can just picture the hose clamp version.....

I gotta stick with keeping it cosmetically original if at all possible though. That's just the way my brain works. I like the challange of the restoration method. That last idea you have with the washers would be pretty close to original look and would provide structural support also. That's the one I'd go with if reattaching the piece falls through. Thanks for the input

I came across the Jigsaw manual and decided to post the attachment page that discusses how the jigsaw in mounted to the headstock of the ER10. It doesn't mention this anywhere in the instruction that I could see but the quill has an arbor mounted on it that fits precisely into the concaved surface of the jigsaw boss that broke on mine. You tightened the quill with the convexed ended arbor up against the boss with a force similar to drilling a large hole in wood, according to the instruction. So, obviously, the repair method I select had to at least satisfy that criteria. The unanswered mystery question at this point is still.....what other forces does it see in use. Is there an up force trying to lift it up off the headstock at any time? Just looking at the design, I can't imagine it being significant. With the jigsaw oscillating up and down, should the saw blade jam up in the material (on it's down stroke) it would naturally try to lift the jigsaw up. The question is, are there times when cutting wood with a jigsaw that it would jam on a downstroke? I don't have enough experience cutting wood with a jigsaw to answer that.

What say you guys??

I will be continuing this thread over in the maintenance and repair forum. You'll find it at:

http://www.shopsmith.net/forums/showthread.htm?p=37199#post37199

Mike,

I'm glad you found the instruction sheet as it tells us that this lug can see some load. (See Mounting The Jig Saw- Step 5) It may well be that someone tightened the quill too firmly once or even many times. As Ivan pointed out sometimes the surface of the material can give a clue. Even though we are getting pretty far off topic... I'm attaching a photo of a rear beam cap that suffered a fatigue failure as an example.

[ATTACH]4327[/ATTACH]

The crack started at a double drilled hole and then slowly propagated until the last bit of material failed suddenly. This process can take years. In these cases you will see a series of lines like growth rings on a tree, showing the stages of the crack and then a bright portion where the remaining material failed. The surface in this photo has some corrosion as the plane was recovered from salt water.
In your case the surface is too corroded to see anything.

I think welding is going to be the repair of choice here. The JB Weld repair could be made to work but as Francis said it is easy to expect too much from the stuff. I don't think JB Weld would make for a good long term repair, especially if you plan to get a lot of use from the saw.

Troy