Straightening 1/4" rod?

[old mart]

How about a redesign to have the motor much closer to the head?

[754]

Use a dial indicaor, instead of a Stone Age 2x 4 ..
someone is going to have to explain why you cant straighten a 36 inch shaft in a 24 inch lathe.
if you are trying to straighten supporting only the ends, then yes it could be a problem.

[Bob Engelhardt]

Summary: the trimmer works exactly as I hoped it would, the vibration being annoying, but not causing dysfunction. I built it out of "stuff", as is my preference. Now that I know it works I may splurge on good rod, but I'm gonna' try to get it straight (enough) first.

Thanks for all the replies - good stuff.

[Bob Engelhardt]

How about using a 1/4" diameter drill rod? I have one I bought from Enco years ago. It is a ground rod, very straight and it comes in 36" length. In addition it was very inexpensive, don't know how much they cost these days.
...

The product cost of drill rod, even turned-ground-polished, is very reasonable. The shipping costs are not.

[Bob Engelhardt]

This is the lowest tech method I’ve used successfully. Use thin wood shims under the shaft on each side of the bend on a table or work bench near the edge. Bend up. Using a c clamp at the highest point of the rod, bend the rod till it touches the table. Release and measure. Gradually increase shim thickness and repeat until the shaft is straight in that section. If you start with too thick of a shim you will bend the shaft in the opposite direction so keep reducing the shim thickness until the shaft is straight. It won’t take long to zero in on success as this is a quantitive approach.

I'll try this if the saxophone fixer's technique doesn't work. I used the press & got it much better, but still not as good as I'd like.

[Bob Engelhardt]

Curious what it is as it buzzes to 10K.

If it's a weed eater, toss it and get a new one.

Short answer (I'll post a build later): it's a mini weed eater. The string is only 2" long, so the RPM has to be 8x that of my 16" trimmer, to get the same tip speed.

[Bob Engelhardt]

This is a technique that I have used often for small rods. Works well and should appeal to your cheap side.
This youtube is a decent explanation.
Youtube titled: Saxophone Repair Topic: Straightening a Rod

https://www.youtube.com/watch?v=RvPTAIAF5EQ

[snip]

That is neat!! I'm gonna' try it. I'll use the drill press & avoid having to work around my lathe's 24 inches between centers.

Thanks for link!

[Bob Engelhardt]

Is there any way you could add a couple of extra bearings, a 1/4" shaft supported at 18" spacing and at that speed is a poor design.

........at 36" spacing and.......
What is the device? Very long high speed mixer or agitator?

18": there's a center bearing.

Maybe the next iteration could have more bearings. It would be hard to know how many, though.

[Bob Engelhardt]

McMaster Carr


Inch—1566 Carbon Steel

Lg.	Lg. Tolerance	Straightness Tolerance	Surface Smoothness, microinch	Edge Type	Hardness Rating	Hardness	Heat Treatment	Yield Strength, psi	Surface Yield Strength, psi		Each
36"	-0.03" to 0.03"	0.002" per ft.	8	Chamfered	Very Hard	Rockwell C60	Case Hardened	75,000	250,000	6061K61	$18.59

Not in the budget, especially with the $10(+-) shipping.

[old mart]

I'm surprised at the reactions so far. Am I the only one sweating blood at the idea of a shaft that long with only three bearings spinning at that sort of RPM? Depending on what it's doing it would not take much to cause it to bend. And once it does I can't imagine the vibration that would occur.

Come on BC, try reading post #9.

[rdfeil]

I am with several others... More bearings and a new shaft.

[mikey553]

How about using a 1/4" diameter drill rod? I have one I bought from Enco years ago. It is a ground rod, very straight and it comes in 36" length. In addition it was very inexpensive, don't know how much they cost these days.
We have to realize that rod of such geometry will bend significantly under its own weight if used horizontally. The bearing in the middle would help if it is concentric with the end bearings, otherwise it could make things worse. When we are talking about long 1/4" shaft being straight, we mean local possible bends. Such shaft can be straight only in vertical position where weight does not affect it.

[The Artful Bodger]

I have managed to straighten a few bits of thin material by rolling it between two blocks of wood.

[BCRider]

I'm surprised at the reactions so far. Am I the only one sweating blood at the idea of a shaft that long with only three bearings spinning at that sort of RPM? Depending on what it's doing it would not take much to cause it to bend. And once it does I can't imagine the vibration that would occur.

[rickyb]

This is the lowest tech method I’ve used successfully. Use thin wood shims under the shaft on each side of the bend on a table or work bench near the edge. Bend up. Using a c clamp at the highest point of the rod, bend the rod till it touches the table. Release and measure. Gradually increase shim thickness and repeat until the shaft is straight in that section. If you start with too thick of a shim you will bend the shaft in the opposite direction so keep reducing the shim thickness until the shaft is straight. It won’t take long to zero in on success as this is a quantitive approach.