Front mount flail mower from mid PTO

[Paul Allwood]

I'll throw this out there just in case you haven't considered it.

When you put the tabs on the roller for the flail blades mount them in a helix pattern.
It will self balance that way.
And it takes less hp to power them.

Thanks - I haven't worked out a final layout, but some sort of helix is what I'm planning.

 

[Runs With Scissors]

Thats looking awesome man!

I love those “jigs” that you made.

Very elegant solutions, keep up the good work sir!

 

[Paul Allwood]

Thats looking awesome man!

I love those “jigs” that you made.

Very elegant solutions, keep up the good work sir!

Thanks

 

[Paul Allwood]

I started trying to workout the layout for the flail tabs on the drum on the bench in the shed yesterday. Aiming for:
- Multiple lines of tabs along the drum with each line in some form of helix
- Flails from one line to the next offset to provide overlap so there are no spots that don't get cut
- No contact between flail Y-blades

After trying for a while I gave up and decided to try to model it in CAD. I had only ever used Solidworks but couldn't resolve a license issue so instead I tried the free web-based version of Onshape. There's a bit of a learning curve to get started with Onshape bit the general idea is the same. After spending a few hours with Onshape today I think I already prefer it to Solidworks.

I think I've come up with a tab layout that will work, but it's really hard to pick a view that makes it clear.









I added the Y-blades to the model to confirm that they cannot hit each other. Tomorrow I'll start tack welding the tabs in place and double check that the blades cannot touch.

 

[Paul Allwood]

I marked out the cutter drum and made a start on tack welding the tabs in place today.

Here's the jig I made to hold the tabs in place for tack welding.





Here's one line of tabs tacked in place.





This is as close as the flail blades can get to touching - pretty much matches what I was able to model in Onshape.

 

[Paul Allwood]

All the tabs are now tack welded onto the drum.

3 August 2026

Enjoy the videos and music you love, upload original content, and share it all with friends, family, and the world on YouTube.

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3 August 2026

Enjoy the videos and music you love, upload original content, and share it all with friends, family, and the world on YouTube.

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[Yooper]

Paul, when you weld out the tabs I suggest you stagger the welds to minimize warping. IOW, weld one set and then rotate 180 and weld another set on the opposite end. Rinse and repeat. When done you can put it between centers in your lathe if it’s long enough and weld on some flat stock to balance it. If there’s a business that services car/truck driveshafts that could dynamically balance it close by, better yet.

 

[Paul Allwood]

Good idea re driveshaft balancing shops - my lathe is way too small. There is a place close to home that makes, repairs and balances driveshafts - I'll ask if they can do my mower drum. Thanks for the suggestion.

 

[Paul Allwood]

Made a start on fully welding the tabs onto the cutter drum today. Hopefully I'll get them finished this afternoon.

 

[Paul Allwood]

All the tabs are now fully welded. Unfortunately, the drum warped a little - it's now approximately 2 mm or in the centre.

I made some brackets so I could clamp the drum to my heavy steel bench and spin it to test it's balance.

From the first rough test it's not great. Based on the battery drill rating I reckon it's getting to a bit under 1,500 rpm and shaking the bench quite a bit. It will need to be able to operate at about 3,000 rpm.

I tried again after adding a couple of bolts opposite the heavy side based on a static balance. The problem with the static balance is that I can't tell where along the length the weight is needed. I think it did improve a little, but there's still a way to go.

I'll drop in at a place near home that makes, repairs and balances drive shafts - hoping that they might do a dynamic balance for me.

I might try to press the drum straight and maybe try a better static balance by resting the shaft at each end on a couple of horizontal bars. But this still won't be as good as a property dynamic balance.

I'm keen to hear any suggestions you may have.

 

[Runs With Scissors]

It kinda scares me………but, I like it!!!!

Be sure to put a “beefy ass plate" between you and that thing when she is operational.

We sure would hate to lose you!

Just sayin

 

[Paul Allwood]

It kinda scares me………but, I like it!!!!

Be sure to put a “beefy ass plate" between you and that thing when she is operational.

We sure would hate to lose you!

Just sayin

Thanks. I've got improve the balance a bit before it's operational.

 

[Chanceywd]

Thanks. I've got improve the balance a bit before it's operational.

I struggle with warping when i weld. the backhoe bucket i just made i was able to get the one set of ears to stay straight but it took buying some long hitch pins to align the holes, making spacers, and a lot of clamps.
Many times depending on what it is I will cut at the middle of a bend or warp , open or close it with the press and then re-weld the cut shut.
Probably nothing that would help you unless you could pin it down close to the area you know is out..

Hope you find a solution as I am pulling for you to bring this mower to a fine finish .

bill

 

[Paul Allwood]

I struggle with warping when i weld. the backhoe bucket i just made i was able to get the one set of ears to stay straight but it took buying some long hitch pins to align the holes, making spacers, and a lot of clamps.
Many times depending on what it is I will cut at the middle of a bend or warp , open or close it with the press and then re-weld the cut shut.
Probably nothing that would help you unless you could pin it down close to the area you know is out..

Hope you find a solution as I am pulling for you to bring this mower to a fine finish .

bill

Thanks Bill - I appreciate your support. I've always struggled with warping when I weld. Doesn't seem to matter how many clamps I use.

Given that it's only running out by a couple of mm I'm hoping I can improve it in the press if I'm careful. I'm hoping this will improve the balance enough to make it usable.

I'm also thinking I'll make enough of the housing so that I can mount it securely and try it both with and without the flail blades attached. I'm not too keen to try it with the flail blades attached on the bench.

 

[Yooper]

Paul, with only 2mm of warp on that length you did excellent! I would always remind the young engineers/designers that where there is weld there is warp. You can see the difference between the first and second videos so you are heading in the right direction.

I really like your idea of parallel bars for balancing. Similar to balancing a surface grinder wheel on its arbor.

At this point in your build why not see if you can balance it yourself? Also, do some research on the subject of resonance which can be something that you can mistake for a balance issue when dynamically testing. Good luck!

 

[Paul Allwood]

Paul, with only 2mm of warp on that length you did excellent! I would always remind the young engineers/designers that where there is weld there is warp. You can see the difference between the first and second videos so you are heading in the right direction.

I really like your idea of parallel bars for balancing. Similar to balancing a surface grinder wheel on its arbor.

At this point in your build why not see if you can balance it yourself? Also, do some research on the subject of resonance which can be something that you can mistake for a balance issue when dynamically testing. Good luck!

Thanks for sharing the video. The horizontal bars is what I'm planning to try for a static balance of the cutter drum after I try to straighten it in the press.

 

[Russell King]

You would get a better product by getting it dynamically balanced. There will be a lot of force developed at 3000 RPM so you will need it balanced at its operating speed for best results. You probably could do this all yourself but would need some equipment and probably not worth your time unless you plan on doing balancing regularly. If you are really interested in the subject, there are books by Victor Wowk that are good for understanding the topic like this one:

Machinery Vibration: Balancing, Special Reprint Edition

Get the 1st Edition of Machinery Vibration: Balancing, Special Reprint Edition by Victor Wowk Textbook, eBook, and other options. ISBN 9780071348614. Copyright 1998

www.mheducation.com

It is partially attributable to the warping but probably more due to the weight and placement differences in the tabs and welds. You might need to do some additional balance when you add the blades to it.

 

[Paul Allwood]

Thanks for the comments Russell and for the book suggestion.

My plan at the moment is:
1. Attempt to reduce the warp
2. Try a simple static balance using horizontal bars
3. Build the housing so I can mount and run it safely with blades attached
4. Attach the flail blades and run it to see how it behaves

I dropped in at the place near home that may be able to do a dynamic balance for me. Won't know for sure until early next week when the boss is back.

I also saw an interesting video where dial indicators are used to detect lateral movement in conjunction with a strobe light to enable the "high" point to be located on the shaft being balanced. Looks like a really simple and really clever idea. It doesn't tell how much weight needs to be added, but identifying where would be a good start. If I don't have any luck with anything else this might be something I could try at home, and could probably even do it with the flail blades attached.

 

[Paul Allwood]

So I had a go a pressing the cutter drum to try and eliminate or reduce the 2 mm runout. After a few goes I pressed a deflection of about 7 mm - that was as far as I was game enough to go and it didn't have any measurable effect. The runout is still about 2 mm.







Next step, I set it up on level parallel bars to check and adjust the static balance.



Initially with gentle rolling it always stopped in the same place and that coincided with the high spot I could find when checking runout finishing at the bottom. After lots of tries I found a couple of bolts and nuts added to the low side resulted in pretty good static balance - seems like quite a lot of weight.

I put these weights at the centre lengthwise as I've nothing better to go on from a static balance.



I might try placing these weights at different spots along the length and try spinning it to see what effect it has....tomorrow.