[Azalin]

I have another question regarding to the keyway depth in the shaft. As I said the keyway is 5x5x15mm. The shaft is 40mm dia. According to the calculator on this site the depth on the shaft should be 3.96mm. Is this calculation correct?

[handlewanker]

Hi.....can't say ....been out of the workforce for near on 14 years.....there is a recommended formula in the Machinery's Handbook, the bible of the metal worker.......I have an 11th edition copy dated from 1943....I'll have a look to see what I can find.
Ian.

[G59]

5mm keyway on a 40mm diameter shaft, recommended 2.657mm depth.

Total keyway depth = height of the arc of the shaft(0.157mm) + 1/2 of the height of the key(5mm / 2 = 2.5mm). 2.5mm + 0.157 = 2.657mm

[handlewanker]

OK.....referring to page 546 in my copy it states......the key width should be 1/4 the shaft diam.....the thickness should be 1/8th the shaft diam,,,,minimum length should be 1-1/2 times the shaft diam........this is the adopted standard irrespective if the load on the pulley or shaft is large or small, mainly for interchangeability......this applies to sunk keys.

In my experience, keys are all square type with half of the key in the shaft and the other half in the pulley etc.

The key is fitted in shear....that is it fits closely on the sides and has clearance on the top......aprox .25mm for most key width sizes around 25mm wide.

When the keyway is cut in the shaft, it is measured from the edge of the keyway slot to the bottom for depth using a depth micrometer across the two edges or even a vernier caliper.......the pulley keyway depth is measured from the edge of the slot to the bottom of the slot.

I hope this helps.
Ian.

[G59]

OK.....referring to page 546 in my copy it states......the key width should be 1/4 the shaft diam.....the thickness should be 1/8th the shaft diam,,,,minimum length should be 1-1/2 times the shaft diam........this is the adopted standard irrespective if the load on the pulley or shaft is large or small, mainly for interchangeability......this applies to sunk keys.

In my experience, keys are all square type with half of the key in the shaft and the other half in the pulley etc.

The key is fitted in shear....that is it fits closely on the sides and has clearance on the top......aprox .25mm for most key width sizes around 25mm wide.

I hope this helps.
Ian.

I agree. But, he's not using any standards.

So in his case, 2.657mm deep is what he'll mill 'if' he wants 1/2 the key in the keyseat(shaft) and the other in the keyway(pulley).

[handlewanker]

Azalin.....a keyway is a keyway.......for your purpose I would leave the shaft as is and if necessary recut the keyway in the pulley bore to suit the shaft......the depth is not critical in this instance.

According to the formular I quoted, the width of a square key at 5mm gives you a height of 5mm too, which is 2.5mm per top and bottom......measured from the keyway edge in both the shaft and pulley, plus .25mm top clearance in the pulley.

BTW....the key MUST be a tight fit in the shaft keyway slot and a close sliding fit in the pulley keyway width......the pulley being a close sliding fit on the shaft too.
Ian.

[handlewanker]

Hi, just reread the posts from the key reference..........I though the keyway was already in the shaft and you wanted to open it up etc.

The shaft has the hard case on it that you mentioned, as soon as you penetrate this hard skin you should be able to mill it fairly easily.....it's hardly likely that the entire shaft is as hard as the outside......at least it shouldn't be.

You may have trouble initially getting through the hard skin....possibly you could need a die grinder to just grind a small flat the width of the key on the shaft to break through the skin.

As the end of the shaft is a part of the spindle and is a critical component.....the spindle will be ruined if the keyway venture fails..........I would suggest sourcing an EDM company to burn the keyway in the shaft.....this can give you perfect results.
Ian.

[Azalin]

Hi again,

Sorry for the late reply. I've been busy.

I modified a 3.1kw brushless inrunner RC motor to run this spindle. I removed the magnets from the shaft and the stator from the thin stock housing. Then I cut a better housing with thick wall and metal epoxied the stator to it.

Then I cut a new 12-13mm shaft from mild carbon steel. Hardened and grounded. Again metal epoxied the neodymium magnets to it. Did a test run at full speed. No vibes at all. Runs very smooth.

I'll take some pics this evening.

By the way, I haven't cut the keyway yet. I will do that per your recommendations. Thank you all.

Sent from my GT-I9300 using Tapatalk

[Azalin]

[Azalin]

[G59]

Now video! LOL

[Azalin]

I would suggest sourcing an EDM company to burn the keyway in the shaft.....this can give you perfect results.
Ian.

Interesting. Can EDM do such thing? I thought EDM cut only full depth.

There are some EDM companies in my area actually.

Thanks for the idea.

[RotarySMP]

Nice work on the motor. How much will you have to derate it from 3.1kW, so it doesn't overheat? What RPM does it do?

Mark

[handlewanker]

Hi....the EDM type is called a sinker where the electrode....copper or graphite etc..... is shaped to the shape you need and it progressively sinks down into the metal by sparking it away......works better the harder the material.......many tools are made this way in the fully hardened and finished state as there is no distortion in the burning process.

EDM can produce parts from raw material that has bee heat treated to give the final part without having to machine it and to extremely accurate and very close tolerances.

For the amount of work you've put into the spindle build, I wouldn't think of attempting to mill a keyway in that hard a material without expecting to have some problems etc..........that is not really true if the spindle shaft only has a case hardening skin which can be penetrated fairly easily once the skin is ground away on the site.

A spindle of this nature should be made from a Nickel Chrome alloy steel that will have a tough core and support a case hardened skin and then ground to size etc......... .5mm being left on for the grinding.
Ian.

[Azalin]

Hi Mark,

Specs of the motor I used originally is:

RPM/v: 1050kv
Winding: 1.5Y
Max voltage: 22.2V (6S)
Max Current: 160A
Max Watts: 3100W
Resistance: 0.014ohm
No Load Current: 1.4A
Can Diameter: 39mm (actual motor diameter)
Can Length: 84mm
Shaft Size: 5mm
Weight: 490g

It revs 25k RPM at 24v but the gear ratio of the pulleys is 1:2 so max spindle speed is 12.500RPM. Still too fast. So I may need another motor with slower kv rating or use 1:3 pulley gear set.

The motor does overheat actually. To prevent this I'll cut a water cooling jacket for it. Similar to this one:

[RotarySMP]

Hi Suat,

What is the temp limit for these motors? The glass transition temp of the epoxy, or do the rare earth magnets start losing strength before that?

Mark

[Azalin]

Mark,

I don't think these motors are temp resistant at all because of the high current flow (mine draws 160 amps max). Proper cooling is a must.

[handlewanker]

Hmmmmmm.....1:3 pulley ratio to get the speed down to 8,500 rpm and a top amp rating of 160 amps.....wow that is almost a starter motor spec.

I have to wonder if the motor can operate at 24,000 rpm when fully loaded at 1:3 reduction and drawing 160 amps.....the power supply must be huge.......my arc welder has a 50/70 volt 200 amp secondary and that has a duty cycle of only 25%.......am I missing something here?
Ian.

[Azalin]

Yes, Ian. You are correct.

I wired two server PSU's in series. They are 75 amps 12v each. Together they give me 24v 150 amps.

I'm using mine for 2 years with no problem but there are cons and pros on connecting two power supplies together. Some say it's dangerous and some say it's not when you take the precaution. Here's a good discussion: Using two power supplies for higher voltage/capacity chargers: safety issues - RC Groups

[RotarySMP]

How does 2x 12V 75A PSU (900kV) in series give 24V 150A.(3600kV). It will give 1800 kV (24V 75A) max wont it?
Mark