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Advice on repair for machined woodworking rotor

Rihards Aigars

Plastic
Joined
Jun 16, 2020
HelloI have run into the problem of cracked woodworking knife holding rotor and would really appreciate opinion of professionals. Machinery has been in service since 2007 and has been used for 16 hours a day since that. It is most likely that this part should be replaced sooner or later as it is under immense dynamic loads and possible that cracking has occurred due to metal fatigue. I am currently looking for a temporary repair solution, so that I could delay purchasing of this expensive component. What I know is that the disc is made out of C45 steel and as I understand this grade of metal hardens if any thermal effects are applied. This eliminates the option of simply welding , as the hardened part would most likely crack again. I have been thinking about some machined solution for keeping the crack closed and preventing it from moving around. I have thought about using lock n stitch threaded inserts. What would be your opinion and take on this problem? I can mention that the disc is 1300mm in diameter, about 50mm in height and weighs about 400kg. Also I will try to attach some pictures of the crack, sketch of the cracked place.
WhatsApp Image 2020-05-15 at 15.46.51.jpgWhatsApp Image 2020-06-02 at 13.59.44.jpgWhatsApp Image 2020-06-02 at 13.59.44 (1).jpgWhatsApp Image 2020-06-02 at 14.28.35.jpgWhatsApp Image 2020-06-02 at 14.28.35 (1).jpg
 
Looks like a wood chipper?

Scrap and replace - you're playing with a grenade.

You've had 13 years service out of that machine, don't be greedy and kill someone.
 
Do some digging in Google about blowing up flywheels in the old days - and the fantastic damage and human cost such caused - that is exactly what is going to happen

On top of all that is the sudden imbalance that can ruin your likely expensive equipment

You need some actual "inspection" like have the RT ("xray") man come in and see how bad it actually is

Go do your lock out / tag out and leave it that way until you know for a fact you are not about to have a disaster
 
There is no way that crack is just out in the rim. Once that piece cracked there it would have stressed the hub and I'm sure you have micro cracks now in the hub. People have tried repairing bandsaw wheels that did the same cracking and it never works in the long run. I'm not sure how the knives are held in your wheel but I'd bet that the metal fatigue is actually caused by not sharpening and honing the knives often enough. Instead of cutting the wood fibers the knives are being smashed through them and it's over-stressing the wheel.
 
I’d guess 6000g on the periphery (definite guess as I can’t remember my omegas from my deltas) I wouldn’t like a 3 lb chunk hitting me
Mark
 
I have thought about using lock n stitch threaded inserts. What would be your opinion and take on this problem? I can mention that the disc is 1300mm in diameter, about 50mm in height and weighs about 400kg.

Nooooooo! There should be around 400-500 hp (300-375kW) driving this. C45 (IIRC) is similar to 1.1191, or 1045 steel. It's carbon steel and will harden if heated and cooled quickly, But your point about fatigue is correct. Even if a lockstitch would fix the immeidate problem, the other slots in the disk are probably getting ready to crack as well. Lockstitching a 1.3m diameter, 400kg disk, with discontinuities, operating under shock load, at (I assume) 1000-2000rpm... Noooooo!

I know that these are damned expensive, but after all those years its time...

BTW, for fun, here's a 2.1m disk weighing about 3600kg. Driven by a 783kw engine...

19-02-37-234533fc-0ad2-4cee-8317-c0e0ed6a4be3.png
 
woodworking cutterhead

I imagine your speaking of a cutterhead for a jointer or planer. Do not attempt a repair, remove it and toss it out. A broken cutter head can throw the knives, let alone more pieces of the cutter head.
mike
 
I do not agree that it is necessarily a bad idea to fix this thing....If you completely disassemble it, Magnaflux and/or X-ray it to be certain you have found all the cracks, properly vee them all out and weld with proper pre-heat, proper alloy, and proper post-heat, then re-heat-treat or stress-relieve, then re-machine to correct warpage, and re-balance...

A new one does not sound so expensive any more, eh?
 
I do not agree that it is necessarily a bad idea to fix this thing....If you completely disassemble it, Magnaflux and/or X-ray it to be certain you have found all the cracks, properly vee them all out and weld with proper pre-heat, proper alloy, and proper post-heat, then re-heat-treat or stress-relieve, then re-machine to correct warpage, and re-balance...

A new one does not sound so expensive any more, eh?

You could probably make a new one for less than welding and X-ray, etc. with a lot less insecurity.

Bill
 








 
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