Cutter and toolholding

Posted by: @pylonuk

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In Michael Campbell's excellent presentation, we talked about tool holding (collets) and cutter suppliers.

I have found that Fahrion collets are excellent quality and whilst fairly expensive by hobby standards they are still accessible in price terms. They are sold by D&J Workholding (Witney) Limited (djworkholding.co.uk)

Regarding cutters, there is a company called Drill Service in Horley who have good quality cutters and excellent service via their webshop. ROUTFISH - Carbide Spiral Flute Router, Fishtail point (drill-service.co.uk) the Routfish  cutters that I have linked to are a great cutter for modelling work as they will cut both wood and composite materials like G10 glass and carbon sheet.

Thanks Barry for posting this.

Regards

Michael

Barry is there a reference table, book or spreadsheet, which tells me what kind of cutter to use for what type of material and type of machining operation.  Also the different feeds and spindle speeds for each material / job combination.  For example to make an auto gyro rotor blade I need to mill an airfoil section onto a 3 foot long piece of hardwood.  So my guess would be a ball nose cutter to do the top curved airfoil section (Clarke Y) - flat bottom so clamped down to the bed.  Then if I was to mill longitudinal grooves for vac bagging carbon tows in it top and bottom, I would need a flat bottom end mill.  If the material I used was 10mm thick G10 3 feet long instead of hard wood, what different cutter do I need?  As I need to buy all my milling cutters drills etc for the Stepcraft mill.

@john-minchell Hello John, some people give good reviews about an app called CNC Cookbook, as you can imagine it is a kind of machining recipe app.

My experience of using lightweight machines such as that we are talking about is that recommended feeds and speeds can go out of the window. So I find these feeds and speeds to be more machine-dependent, rather than cutter and material dependant when using hobby machines.

If the rotor blade you mention was hardwood then HSS steel cutters (really just metal cutting end mills)  will work OK, but they will only last minutes on G10.

For G10 it is essential to be using carbide cutters and it may even be that you would use one cutter per blade.

Don't discount using end mills with say a 1mm corner radius (6mm x 1mm CR) as these would work well in the step craft for doing the blade. The advantage of these tools is that for a large part of each finishing path cut then you are sweeping over the previous cut with the flattish part of the end mill. For finishing use a planar cutting strategy going from the leading edge to the trailing edge and vice versa, use about 1mm step overs (maybe 0.5mm if you are patient).

Also consider using an intermediary finishing cut after the roughing cut, so leave max of 1mm stock on after the roughing cut (better with around 0.5mm stock) then an intermediary finishing cut with around 0.25mm stock left and then the final finishing cut, in a two stage finish the cusps from the roughing cut can still cause tiny flexing in the machine, this is minimised with the three stage approach.

Woods and composites have a very wide range in which they will cut with good results (RPM and infeed), metals less so and particularly stainless steel and titanium. stainless steel seems to be worse than titanium and what happens is that the material can work harden ahead of the cutter with disastrous results.

Tell me a bit more about the material and machine power and I will give you some feeds and speeds out of my cutting database.

Regards

B.

Thanks for your reply Barrie - very useful.  I will purchase a selection of milling cutters from Drill Service as per your recommendation.  As far as the power of the mill I have I am not sure what I can tell you other than it is a Stepcraft D840 and has a HF500 (500watt) spindle motor which uses HF11 collets & 1mm up to to 8mm bits.

The original auto gyro rotor blades were in 2mm thick plastic folded over to make the aerofoil section with a 10mm square aluminium box section running the length as a spar.  They fracture where they are bolted through the blade and aluminium at the root where the stresses are concentrated attaching to the rotor head.  So my idea is to manufacture them in hardwood which will be easier and about the same weight but stronger where the through bolts are at the root attachment point.  May possibly need to machine top and bottom channels for CF spars reinforcement, then drill a couple of holes to put epoxy the balance weights into.  Then cover with heat shrink tubing to finish.