homemade Wood Router - project failed And almost got me seriously injured- READ DESCR

⛔⛔⛔ warning! You must not try the next project! Before you read the description! ⛔⛔⛔
Dear friends, I started this project with great enthusiasm and everything went well. I did not do something that is not typical of me, and did not take into account some simple laws of physics.

At the request of some of my followers, I decided to make a video showing how to turn an angle grinder into a Wood Router. I started planning the steps and started working. Everything was perfectly built except for one thing. I did not take into account the speed of the whet motor, the rotation speed was too high!

My mistake was that I had to install a speed regulator and lower the engine speed. This would prevent the main axis of the engine from breaking! And the result you will see in the video In the 09:24 minute. Although the project failed I decided to upload the video so you can see how dangerous it can be when you do not keep the safety rules at work.

Dear Friends Safety at Work First of all !!! Smart people will watch the video and learn a thing or two about the importance of safety at work especially after changing its purpose to an electric tool. And this is the first project I failed and Today I learned an important lesson and it is definitely .a sad day for me! Tell me in the comments what you think it will help me greatly

https://www.youtube.com/watch?v=Bo7ovTxEprk

Thank you for sharing and posting the video. I am sure if we were all honest we have all had near misses in the workshop when we have not thought about design or the consequence of taking short cuts etc. But this video is a great reminder on how dangerous both woodwork and engineering tools can be and we all should watch this video once a month
Again thank you for posting and glad this was only a near miss
The Home Engineer

Thank you very much for your support

Hey dude, thank you for having posted this video. In my humble opinion the problem was not the speed, but the lack of support. The axis did break at the bearing point, may be because an excessive oscillation or more likely because the bit touched a vein with a sudden change in friction, because these shafts are hardened they are also quite brittle. Slowing down the speed would had not helped, on the contrary might have worsened the risk actually.
The problem could have been avoided by making a second bearing holding a much more ductile shaft that in turn would have held the mandrel. This last shaft would have absorbed vibrations and pressure shocks coming from the contact of the bit with the wood. Again, this is my modest opinion, I am not a mechanical engineer after all :)
Repurposing electric tools is cool but could be a serious danger as we do not know the calculations the engineers did when they designed the tool.
Glad you were not injured seriously.

Cheers & stay safe,
Claudio

I didn't see that coming! Even though you said it would happen at 9:24 I still jumped out of my chair. Very scary and luckily you were not injured. I've never video'd my projects so my major fails have gone undocumented. Fortunately I have learned more from my fails than from my successes. My homemade table saw is without doubt my most potentially dangerous piece of kit that I have created but has served me well for the last 12 years. If it does ever fail I hope to learn from it.... otherwise I'll be 6 foot under.

Impressive amount of bouncing around from chuck. I guess it was too far out of balance for ~ 30,000 rpm? You could probably machine whats left of the rotor and fit a mini collet chuck into it?
It would still be spinning way too fast to use anything over 1/8" ~3mm dia carbide but may work for engraving/

Chuck too heavy and put too much torque on the shaft and the shaft was too hard for the cutting shocks from a router bit.

People that don't make mistakes don't make anything else either. My last project came out meh. Like you I went into it pretty excited for decent success. It just didn't end up how I'd hoped it would. Was a router base too.

I watched the video at 3x speed right up to the point when you installed the router bit then dropped the speed to .25 even at that speed when the chuck came free it was near relativistic speed. I even viewed it frame by frame in less then 2 frames the chuck was there then it was gone.
Thanks for sharing this video really brings to light the things that can go wrong even on well thought out builds.
Like was stated a slightly extended nose to the grinder with another bearing and a shaft extension could and would help.
A long time ago I had a 5" angle grinder that the gears wore out in this was a 9 amp grinder so it was quite robust about 2/3rds the size of the 9" grinders
I had been needing a pencil type grinder for a while so I made a nose cone out of aluminum billet about 5 inches long and a shaft with 5/8 11 thread to accept the cone and cob stones most are rated for 24 to 36,000 RPM and I bought only the better grades anyway. I used 2 bearings in the nose cone and a short coupling to connect the motor shaft to the arbor shaft the grinder lasted me for many years pre grinding welded up bearing bores before I line bored them

wow , could have turned out a lot worse than the tool breaking

What broke? The chuck just flew off. That's to be expected. Some JB Weld-It can fix that right up.

Thank you very much dear friends for your support and detailed comments. I learn from each and every one of you and this is an amazing site !!!

The start of your build looked reasonable but I knew what was coming as soon as I saw that drill chuck being attached, not meant for side forces thats why all routers use collets. A classic case of enthusiasm getting the better of judgment but I am sure some of us have visited that place.
Thanks for posting that warning lesson to think more before you leap.

I have a RotoZip tool that has a factory 3 jaw chuck on it. They're 30,000 RPM so as fast as most routers go. Dremel makes a 3 jaw chuck for their rotary tool too and it works. Collets can be made a lot lighter than 3 jaw chucks can be and theoretically they have a better grip. We all know what Yogi said about theory and practice though. All of this did get me thinking about a spindle for my CNC machine. I don't want to shell out for what a water cooled spindle costs. But I'd probably run an ER16 collet on it.

The only wrong thought anyone can have is thinking that they can think of everything. You just have to try stuff and see how it really goes. Because often in non-trivial matters it'll likely be a lot different than you think!

After a test I did I came to the conclusion that the converter was broken because it was very thin about 6mm and it was broken just in connection with the wheel

You mean the adapter was damaged?

What is broken is the axis of the engine
Tomorrow I'll take a close-up of what's broken

Oh you mean the motor shaft? The bit that sticks out of a motor and spins is the shaft. Though it does rotate on an axis I suppose. That's bad if it broke. The chuck must have really been out of balance.

Yes, probably everything was balanced by the time I touched the tree

You are right about that. Touching the tool to the wood may have balanced it good for you. :)

Most people find it difficult to say I messed up but this post has probably taught a lot of folks a most valuable leson. Thanks for a visual warning, besides the shaft failing the rest looked great

Even if it worked them return springs were too light. I know stock they're too heavy but what I saw here is too light. I got three commercially manufactured plunge routers. You have to push them pretty good to get them to go down. Just how they are.

Hi
Another issue is side loading a drill chuck.
This is also why you should never mill using a drill chuck as they are not designed to take side loading. I have seen several people snap chucks off arbours while milling. One was my boss :confused: last year.

I am curious if the motor shaft had a flaw in it. By putting the chuck on it with a sideways load, it wasn’t designed for, that caused it to fail. One of the 2 would be my guesses. But I am not an engineer.

I've heard you should never side load drill press bearings. I mill with a 3 jaw chuck in my mill all of the time. Not a problem. I have collets for my mill too. Just not enough. The last slot I milled the day before yesterday I put an end mill into my drill chuck. I don't have a 5mm collet for my mill. I needed that slot milled though. I didn't know if that end mill could cut steel, or not. It was an el cheapo import jobbie I'd bought for my CNC engraving machine. I have all of the collets for it. It only has an ER11 holder though. And there's little chance it can mill steel. I never tried and I doubt it can. It's a soft materials machine. Wood, plastic, stuff like that. Maybe some aluminum. The OZ25 on my mill is a bit harder on the wallet to fill out the set on. I'm thinking about picking up an ER32 holder for it. I could get the holder and a 9 collet set for about what 3 OZ25 collets would cost me. I feel burned either way so I haven't done anything. I've heard some bad things about some of them ER32 holders too. Which makes me leery to get involved. I know my OZ25 holder is good. I've been using it for decades now. Collets for it are just so damned expensive though.

Diyfixman,

I don't think the speed was too fast for routing, just too fast for your under spec'd connection with a too heavy lump of non-concentrically turning metal. Tiny, short shaft, loosely fitting sleeve, held on by set screws. Couldn't expect that to resist all the forces trying to tear it apart. Because of the length of your chuck and bit combination, the effect of the first little bits of deflection, due to imbalance and the load on the cutter, rapidly became magnified and ran away. Lee

The failure was predictable. Here is the offending frame from whence the chuck flying off the shaft was inevitable:
Attachment 31652
You see here the chuck being fastened to the shaft using an Allen key.
Thus:
1. there is no means on the shaft to prevent the chuck travelling along the shaft, except friction.
2. When cutting, the shaft will flex, setting up a pattern of (rotary) vibration. This vibration is enough to cancel the friction force holding the chuck in place. --> BOOM

I have had the same issue on several of my routers when using 1/4" tool bits. None of the bits flew off, but they dug deeper and deeper into the wood - until I noticed and switched the machine off. Tightening the collet harder did not help at all. Sharpening the bit did help, however, at least for a while. Only one action eliminated the problem entirely: use bits with a 1/2" shaft.
So far the observations. Once you consider that halving the diameter of a shaft makes it flex eight times as much, and that chattering of a tool arises whenever the forces acting on your tool times the lever arm exceed the stiffness of your setup, you have it.

There is no indication in the video that the shaft actually broke, nor that it bent either. Thus, I take it that the shaft came out unharmed, and that the use of "broke" is an exaggeration ascribable to the shock of the failure happening. Further, there is no reason for Makita engineers to specify a steel with 0.8% carbon or even more to make a shaft that can fail by brittle failure. Why use steel with a yield stress of 2000MPa (about 60 Rockwell C) if 500 or 600 MPa, or twice that of mild steel, is more than enough? But there is plenty of reason to make the shaft thinner than 6mm, 5mm perhaps, or even 4.5mm. Maybe diyfixman can provide us with this kind of information?

Quote:

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Originally Posted by CanBeDone

There is no indication in the video that the shaft actually broke,

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If you read carefully at the end of the video you see the shaft is broken. Even the OP confirmed it in a previous comment.
But you have a point about the allen screw fastening (I didn't thought at it at first sight): that certainly induced a vibration (an oscillation of the moment with the fulcrum at the bearing) that made the shaft subject to a pulsed shear/bending force exacerbated by the contact of the bit with wood that, because its veins, induced further variations in the moment.
This could have been coumpounded and potentially resonate, increasing on some instants the peak of said shear force.

About the motor shafts, these are usually thinner in universal motors to reduce instabilities and increase lighweight when they are meant to hold axial forces only. In the industry it is usual to make these shafts with a particular grade of steel (that vary among manufacturers) able to widthstant the axial force despite the reduced section. Also AFAIK often they haden the steel (not as a file, though) at the location where the shaft will be in contact with bearings: I've seen a manufacturer of wiper motors that uses an induction coil to harden the steel where the shaft will mate with bearings.
I am not an expert in metallurgy neither a mechanical engineer, but my experience was that motor's shafts generally are harder that C45 steel and brittler, far less than a file though. So I do not dispute your reasoning about the choice of steel, actually I second: the steel will be likely somewhat around 700-900 MPa, thinner than what it should have been if it were meant to withstand mixed, pulsed forces, and this is a further reason to see it broken when a pulsed shearing force is applied to it.

EDIT: Grammar.

Quote:

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Originally Posted by pfredX1

People that don't make mistakes don't make anything else either.

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I added bold text to pfredX1's quote;
Many variations exist with that sentiment phrased differently; this is now my favorite.

The one that gets me is the Chinese proverb, Success is falling down seven times and getting up eight. It has a ring to it that resonates with me. Says a lot, you know? Sure you might get the stuffing beat out of you but if you persist and overcome then that's a true demonstration of character.

Agreed. No matter how many proverbs exist, I'm convinced they are repeated in most every language. Seems cultures who've endured a fair share of hardship are most prolific. My favorites, Romanian and those from our own West.