Bespoke CNC

[Prop Man]

Thanks for your reply Phil. It is very unusual to make 2 propellers the same. We make 2-3 a week and business is growing. I design the propellers mathematically then I draw them using Rhino. Then I pass the 3D drawing and the lump of wood to the machinists. I have looked over the shoulder of the company doing my machining and the CAM software doesn't look that complicated, the sort of thing I'm sure I can learn. At the moment I am spending about £25K a year on machining, it certainly makes commercial sense to gain such capabilities as it is a major part of our manufacturing process.

I'll be happy with a tolerance of 0.2 mm.

At the moment they are being made on a large 3-axis Thermwood, which seems to do the job well but the job is taking about 6 hours per prop including programming. I believe the machining time can be speeded up considerably with better tooling and fixtures. The loads on the cutter are quite high and the tool has to be extended from the holder by about 150 mm in some cases to gain clearance from the work. I'm supposing that a 3-axis machine will have better rigidity at the spindle, for such big heavy cuts when roughing out, on a pretty hard wood. I'm looking for a 20 mm tool holder, again to help minimise resonance.

How do you think a 4th axis will help the job?

Keen to enter discussions with anyone with track record building large-ish machines who can take on this project.....

-Prop Man

Prop Man,

Are all the propellers the same, who currently does the cad/cam

Just learning the software can take a long time, you would need 4 axis and the software would cost around £5K +

What is the tolerance on the props, how many do you need to make.

When/if you make them yourself and you screw up YOU PAY.

I'm sure a lot of peeps on here could make this, me included but don't know a dedicated company that makes them.

Phil

[M250cnc]

Prop Man,

4th axis means a rotational axis, and it would seem to be impossible to do this without a rotary ?

Heavy cutting means potential for movement/deflection of the prop

Are they doing this with one cutter setup, this is where expensive software can cut down machining time as well

Maybe post a sample file to show the size/shape of what you are after

Phil

[Prop Man]

Phil,

Do you mean rotation of the work for the 4th axis? If so, the work is turned over manually. The propeller blades do suffer from resonance when the finishing cut is being performed on the second side as there is little material left. The work is held in the centre and at each end by the parent material, which is cut away once the process is finished. In addition, wooden wedges are jammed between the bed and the work, about half-way down the blade for the final cut on the second side to add rigidity and improve the finish.

I have some good ideas of how to build a much improved fixture system which allows the work to be well supported and rotated manually along it's long axis to machine the second side. Fixture building is something I will do as I have the capabilities and experience to do this.

They are roughing it with a 25 mm braised tipped square cutter and finishing with a replaceable HSS bladed cutter with a radius on the corners.

I'll try to work out how to put some pictures up. Propellers range from around 50" long to 95" long. The blank starts off as a square section and most of the material is removed during machining.

Prop Man

[Prop Man]

Pictures of the Thermwood cutting a propeller in the 'galery - albums' section.
-Prop Man.