Straightening drive shaft on Monster Mill?

[IslandLizard]

A couple days ago I had the misfortune to bend the drive shaft.
Has anyone straightened one of these? Any suggestions on how to do that best?

The wobble is about 1/16", measured at the end of the 2" long shaft. The bend must be in the short 3/4" section between the front of the chuck and the bearing.

Victim:

• Monster Mill MM2
• 1.5" regular steel rollers
• 3/8" integral drive shaft
• Driven by HF 1/2" Heavy Duty Low Speed drill

I inquired with the manufacturer and he can supply a new drive roller, even with an upgrade to the 1/2 inch shaft and bearing.

It's got almost 2 years of fairly light and flawless use. It's definitely not worn out.

Setup details:

• Standard factory medium density fiber baseboard and hopper.
• The mill is mounted with the drive shaft toward the center of the base board, per installation instructions.
• The mill is driven by a Harbor Freight 1/2" Heavy Duty Low Speed drill (SKU93632), which many people use. The drill is mounted upside down, handle pointing upwards. It's an almost perfectly tight fit between the base board and the (top) housing of the drill, creating a decent seating for it. There's not much space for the drill to move, except it can rotate sideways, which is the culprit to the problem.
• Distance from front of chuck to the bearing: about 3/4"
• Protruding shaft length from bearing: 2"

Once fixed I'll definitely fabricate a different drill mounting method, most likely using a larger plywood base and a cradle for the drill so it just can't move in any direction. That drill is a beast that chews through almost anything.

 

[madscientist451]

First impression is that you won't be able to straighten the shaft, you need to install a replacement shaft. Another option would be to cut the shaft where its bent and install some type of coupler to extend the shaft so you can fasten the drill to it. If you have to take the shaft off, it might just be better to install a new one. You probably have to remove the shaft and use a metal straightedge to see where it's bent.
I don't have one of these mills, but I've bent and repaired shafts on bigger industrial equipment so I'm basing my experience on that.

 

[ChelisHubby]

If you have a friend with a lathe and a dial indicator it can be straightened but the average joe with hand tools will be better off buying a new shaft.

 

[IslandLizard]

It looks simple, but after some searches on the web for straightening shafts there is some serious equipment involved to do it right. But I don't need micron precision. Even a hammer, some angle iron and/or a vice could improve the situation. The bend must be in the first 3/4" from where the chuck ends and enters the bearing in the block. The first 1 3/4" were inside the chuck. I have a straight edge, calipers and a micrometer, no machinist dial, lathe, or press.

The roller and shaft are integral, with the turning centers still on both ends. If the shaft were screwed in or splined it might have been easier. That steel is not very strong or rigid at that diameter.

 

[riderkb]

I have a lathe. If you are not in a hurry and are willing to risk it I can give it a whirl.

 

[masskrug]

Out of curiosity, How in the &*#! did you bend it?

 

[IslandLizard]

Out of curiosity, How in the &*#! did you bend it?

It's HBT, I was expecting that question.

Gap was set at around .026" for small grain, using my AE credit card gauge. Upon starting the mill, with a pound of softish grain in the hopper (Golden Naked Oats), it immediately jammed, turning the mill 90° dumping out the grain. No big deal, got plenty of grain.

After this unexpected event, I noticed the drill itself had turned quite a bit from being perpendicular to the baseboard, gouging a void into its edge. As all of you MM owners know, the factory baseboard is made from softish MDF, not my choice of material, and never really liked it, but heck, it came with the hopper.

Upon further investigation to see what caused the problem, I found the slave roller was stuck, wouldn't spin by hand whatsoever. After loosening the set screws, moving the gap adjustment knobs, and resetting the gap it then spun freely. Test run without grain... I noticed the wobble.

As we know, the drill has plenty of torque and the resistance from the base board caused it to wedge, bending the shaft. I acknowledge now, more than before, this is a really, really bad way to mount the drill. Let this be a warning for all of us!

I'll post some pictures later, got to finish this old ale first, and maybe another one, to be able to do that.

 

[IslandLizard]

Thanks to 2 HBTers who offered advice on how to straighten the drive shaft, it's back within usable specs again. One explained the basic process and the other even reached out over the phone, pointing out the nitty gritty, walking me through the steps. That was truly wonderful! :rockin:

Next up is making a new and enlarged base board so that the drill can be cradled much better, preventing it from turning ever again which bends the shaft. That should have been done from the beginning. The standard factory board that comes with the hopper is way too small for that purpose.

Thanks for all the help and support, guys!

 

[EZCyclone]

Thanks to 2 HBTers who offered advice on how to straighten the drive shaft, it's back within usuable specs again. One explained the basic process and the other even reached out over the phone, pointing out the nitty gritty, walking me through the steps. That was truly wonderful! :rockin:

Next up is making a new and enlarged base board so that the drill can be cradled much better, preventing it from turning ever again which bends the shaft. That should have been done from the beginning. The standard factory board that comes with the hopper is way too small for that purpose.

Thanks for all the help and support, guys!

Fritz, I'm very glad we could get it all back into working shape. Remember that baseboard was not designed for the stated purpose. It was designed to fit into a box that was cheap to ship. :cross:

Better go get your brew on.

 

[IslandLizard]

[...] Remember that baseboard was not designed for the stated purpose. It was designed to fit into a box that was cheap to ship. [...]Better go get your brew on

That's exactly what it looked like. Dusting off the router now...

Arrogant Bastard clone is waiting to be milled. Yeast starter has been ready for days.

 

[Snicks]

I bent the crap out of my monster mill shaft last weekend too, what method did you end up using to get it back? I smacked it a few times with a hammer and judging by eye to get it slightly more aligned, but its far from perfect.
I haven't had a chance to try a full bill of grain in it since, I'm a little concerned it will sieze up or wear out my drill.

 

[IslandLizard]

I bent the crap out of my monster mill shaft last weekend too, what method did you end up using to get it back? I smacked it a few times with a hammer and judging by eye to get it slightly more aligned, but its far from perfect.
I haven't had a chance to try a full bill of grain in it since, I'm a little concerned it will sieze up or wear out my drill.

Darn! Sorry to hear that. Did your drill also flip when the mill locked up, wedging itself against the baseboard? That's a flaw in the mounting directions. And dangling an unsupported heavy drill from the bare shaft is not good either.

I carefully marked the high point and used a short piece of oak flooring on end and a hammer to force it down slowly to straighten it. The place where you bend it back is important, and you may need to create a support (fulcrum) to control the bending point, to prevent an S-shape in the shaft. I got it close but not perfect, a slight wobble remained. Read on.

After re-mounting the drill, now sideways and on a better baseboard, and slowly running it, I found the deviation, because the drill itself moves a bit sideways in response to the bent shaft. Using the drill as a handle, I ever so slightly and carefully bent (eased) the shaft back until the wobble was about as gone as could be. It took a few small tweaks.

Then after milled a few pounds, I noticed that a slight wobble had returned. Easy to correct again, the same way, but it makes me wonder why that happens.