Choosing a material for a mill handle

[Bob Busby]

Hello. MechE noob here. I'm an ECE guy and I'm apart of a group of students working on a solar car. I decided I wanted to get more mechanical experience so I joined one of the ME teams. However, before they let you work on real stuff they make you go through smaller projects.

So my first smaller project was to make a mill handle to replace a broken one. I designed it in Solidworks. It is extremely simple, just two cylinders connected to each other with the radius of one much smaller so it can fit into a circular slot.

My question is how to choose a material. I haven't the slightest idea what factors are at play here and how to go about deciding. I figure it will be plastic or aluminium but that's all I've got.

Can I have some guidance as to how to go about this? Any help would be appreciated.

 

[rollingstein]

How much load does it have to bear? Does it have to be light? Aesthetic or functional?

How are you planning on making it? Machine it from rod stock? Mild steel is often a starting point. Or stainless steel.

Plastic is an interesting choice. How will you get the right shape for a one-off plastic component? 3D-printing?

Will it be exposed to hot objects, even accidentally? Or solvents? Then plastic might be a bad option.

Is the fit an interference fit or are fasteners involved? If a weld then weldability is a concern.

 

[Bob Busby]

I don't know how much load. It's operated by hand so I guess however much a person can apply. How should you measure this?

We were planning on using a lathe to make it. I was thinking of just buying a rod. Can you not use a lathe for plastic?

I was thinking of tapping the smaller cylinder so that it could be fitted with a screw. Nothing fancy like welding. Aluminum is good enough for this, right? Are there any other concerns I should be aware of?

Thanks so much!

 

[nvn]

Bob Busby: What is the material of the broken mill handle? What type of mill is it? Mill can mean so many things. You probably would want the new handle material to be stronger than the broken handle material.

Can you post a dimensioned sketch of the mill handle assembly? This might enable us to try to answer your material selection question. Also describe where and how the handle broke. Annealed stainless steel SAE 304 might be a possibility (although it has rather low tensile yield strength).

 

[Bob Busby]

I'll try to get the information you requested as soon as possible (it might be a day before I can go back to the shop).

In the meantime how will knowing these things guide your decision (I'm trying to learn, not just get an answer :) ). I don't think tensile strength will matter because the rod will only have a compressive force applied. There's no reason to pull the handle.

 

[nvn]

Bob Busby: That brings up a good point that I forgot to mention in post 4. On the dimensioned sketch, also include the dimensioned location, and direction, where the applied load is applied.

The necessary material and cross sections depend on, among other things, the handle stress. The stress depends on the assembly dimensions, and how the handle is loaded.

Right now, until we see a sketch or picture, we do not know what load and stress the handle is subjected to.

I don't know how much load. ... How should you measure this?

If you have no better way, as a last resort, perhaps try to use one of those household scales people weigh themselves on. Try to get your body in the same position as when you apply load to the mill handle. Then try to press on the scale with the same force one would apply to the mill handle.