Comments sought on new build: A CNC Router for RC Gliders and Planes

[njhussey]

One thing I'm happy with is the Z axis. I was expecting to have to loosen bolts on the Y & Z axis to adjust the spindle to get it at 90° to cut flat. I did a pocket with a 0.4 stepover and it was so smooth I reckon that by sheer bloody luck the spindle is almost exactly at 90°. When I surfaced the bed this morning (pocketing at 7000mm/min, 6mm 2 flute coated carbide bit at 0.4 stepover and 0.5mmdepth of cut) I couldn't notice any ridge at all, totally smooth.....jammy bugger, makes up for the broken tap in the base!

[routercnc]

Sorry to hear about the tap! So annoying and as they are very brittle it's not easy to tell that they are about to go.

I've seen them spark eroded out, but it takes ages and I think is done underwater (?!).

I've had success with Jazz's method of pecking it out with hard tools and getting lucky until I could unscrew it. Sometimes there's enough sticking out to get a mole wrench on it, but not with yours.

If you definitely need the hole at that location and it won't budge then one option is to use the CNC machine to cut out a large through hole around the tap (say 30mm diameter) so that a nice round cylinder of aluminium is removed containing the tap. Then machine a round pocket (say 60mm diameter and 5mm deep) centred on the same hole. On the lathe turn up a part which fits the 60mm dia pocket and has a shank of ~30mm which goes right to the bottom of the hole -essentially a plug the same shape as the removed material. Drill a couple of countersunk holes (to keep the bolts flush) into the top flange of the plug, and through into the bed. Tap the bed and bolt the plug in place. Then drill and tap the centre hole again with a new tap!

Another option if you manage to get the tap out but damage the thread too much is to use a heli-coil which uses as oversized tapped hole to insert a spring shaped piece of metal which then creates the original thread diameter again.

[njhussey]

Sorry to hear about the tap! So annoying and as they are very brittle it's not easy to tell that they are about to go.

I've seen them spark eroded out, but it takes ages and I think is done underwater (?!).

I've had success with Jazz's method of pecking it out with hard tools and getting lucky until I could unscrew it. Sometimes there's enough sticking out to get a mole wrench on it, but not with yours.

If you definitely need the hole at that location and it won't budge then one option is to use the CNC machine to cut out a large through hole around the tap (say 30mm diameter) so that a nice round cylinder of aluminium is removed containing the tap. Then machine a round pocket (say 60mm diameter and 5mm deep) centred on the same hole. On the lathe turn up a part which fits the 60mm dia pocket and has a shank of ~30mm which goes right to the bottom of the hole -essentially a plug the same shape as the removed material. Drill a couple of countersunk holes (to keep the bolts flush) into the top flange of the plug, and through into the bed. Tap the bed and bolt the plug in place. Then drill and tap the centre hole again with a new tap!

Another option if you manage to get the tap out but damage the thread too much is to use a heli-coil which uses as oversized tapped hole to insert a spring shaped piece of metal which then creates the original thread diameter again.

Cheers Barry, im favouring trying the smash it out with a hard pointed punch. The annoying thing was that I was backing the tap out the hole...

I like the plug idea, ive got to surface the Ali base at some point so might turn a press fit plug.

[JAZZCNC]

One thing I'm happy with is the Z axis. I was expecting to have to loosen bolts on the Y & Z axis to adjust the spindle to get it at 90° to cut flat. I did a pocket with a 0.4 stepover and it was so smooth I reckon that by sheer bloody luck the spindle is almost exactly at 90°. When I surfaced the bed this morning (pocketing at 7000mm/min, 6mm 2 flute coated carbide bit at 0.4mm stepover and 0.5mmdepth of cut) I couldn't notice any ridge at all, totally smooth.....jammy bugger, makes up for the broken tap in the base!

Why such a small step over neil.? . . . . With 0.4mm it must have took for ever.?

The Acid test for tram is when you use a wide cutter.!! Try 50mm with 75% step over and see what happens.? 6mm with only 0.4mm step over will hide most error. Also cut both X & Y direction.

[njhussey]

Why such a small step over neil.? . . . . With 0.4mm it must have took for ever.?

The Acid test for tram is when you use a wide cutter.!! Try 50mm with 75% step over and see what happens.? 6mm with only 0.4mm step over will hide most error. Also cut both X & Y direction.

The step over was what was in Cambam and gave a good finish so I kept it, yes took a while to surface it. I'm going to get a small fly cutter to do the surfacing in the future so we'll see then!

Going to be spending the next few weeks playing with speeds and feeds on various different materials...looking forward to it

[JAZZCNC]

I'm going to get a small fly cutter to do the surfacing in the future so we'll see then!

Wide cutter will give you perfect finish if trammed correct and take fraction of the time.

Wouldn't get a fly cutter these spindles don't like them. Get one of these with indexed tips http://www.wealdentool.com/acatalog/...nning_928.html

Or if on budget one of these. http://www.wealdentool.com/acatalog/..._Wing_250.html

[njhussey]

Ok cheers guys, ill get one of those cutters, as work is paying probably the more expensive one.

What sort of step over do you guys use?

[JAZZCNC]

What sort of step over do you guys use?

Depending on material and Depth between 50-100% often 75%.

[njhussey]

Well due to my hat at work changing from engineer to Web designer ive not done anything mechanical or electrical to the machine...However I have been cutting bits for an RC Glider in my lunches....



Now to crack on with CAD and finish off some drawings so I can make more models!

[Blackrat]

how are those parts cut ?