Mill Motors

[Engibeer]

Camo,

The lovejoy ones don't appear to clamp to the shaft... I see the ebay ones do.

Are you using aluminium rod with your motor?

 

[Camo6]

Yep. Alu rod with ebay coupler. Drilled through coupler and used shear pin after brew day stuff up with mill.

 

[Lyrebird_Cycles]

I'd have thought the ally rod would act like a shear pin anyway, especially after you drill a hole in it.

 

[Engibeer]

Wouldn't mild steel be easier to drill than stainless with almost equivalent tensile strength?


Ultimate tensile strength mild steel = 841MPa USS = approx. 0.75*UTS 631MPa

Ultimate tensile strength Stainless = 860MPa USS = approx. 0.75*UTS = 645MPa

Ultimate tensile strength Aluminium = 300-480MPa USS = approx. 0.65*UTS = 195MPa (conservative end)

Motor torque = 20Nm

Where J =

τ = T r / J (1)
where
τ = shear stress (MPa, psi)
T = twisting moment (Nmm, in lb)
r = distance from center to stressed surface in the given position (mm, in)
J = Polar Moment of Inertia of an Area (mm4, in4)
Ultimate tensile strength Stainless


Circular Shaft and Polar Moment of Inertia
Polar Moment of Inertia of a circular solid shaft can be expressed as

J = π R4 / 2
= π (D / 2)4 / 2
= π D4 / 32 (3)
where
D = shaft outside diameter (mm, in)

For our example


Tmax =

T r / J















d

12

mm













T=

20

Nm

d

0.012

m

Tmax

58946275

Pa

Tmax

58.94628

MPa







USS, Aluminum

195



FOS, Aluminium

3.308097









USS, SS

645



FOS, SS

10.94217




Aluminium rod would still have a factor of safety of 3.3x based on the peak torque of the motor.

 

[Engibeer]

Sorry, neater formatting on the calcs

Tmax = T r / J


d= 12 mm


T= 20 Nm
d= 0.012 m
Tmax= 58946275.22 Pa
Tmax= 58.94627522 MPa

USS, Aluminum= 195
FOS, Aluminium= 3.308097064

USS, SS= 645
FOS, SS= 10.94216721

 

[zwitter]

Hi
12mm aluminium rod as a shear pin, ha ha ha!

The shear pin has to be strong enough to handle the load but weak enough to shear when the load is exceeded. I used the hole in the motor drive where the shaft connects as the easiest place and just used a 2mm hole in the shaft and then tried copper but it sheared too easily so then tried stainless 2mm welding rod and it has only sheared once since and is cheap to replace.

I used a stainless 12mm shaft as it happened to be available in my metal pile. But could use almost anything even tube would work.

You will need to have a hole in the shaft for the pin. Could ask around someone will have a drill to help you out.

For the coupling you can try without any hole or flat on the shaft or can file a flat on the shaft as I did if it slips.

James
Zwitter


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[Camo6]

I'd have thought the ally rod would act like a shear pin anyway, especially after you drill a hole in it.

It's a grain mill, not a top fueler driveline!

 

[Lyrebird_Cycles]

195 MPa shear strength is for something like a 2xxx alloy in H6 temper. Cheaper 1xxx grades with no heat treatment are as low as 50 MPa.

He said he got the ally off Fleabay, didn't state the grade or temper*. If you split the difference and assume ~100 MPa your factor of safety is about 1.5

Aluminium is also very notch sensitive, hence the comment about the hole.


* And you couldn't be sure it had the grade and temper stated anyway.

 

[mofox1]

Okay, further to the above, I see that MD has the stainless shaft available.

Does this have a hole drilled in one end for the gearbox connection?

I don't own a drill press.

Cheers,

Matt

I got the shaft from MD - no drill press for me either.

After much trepidation, I eventually just bought a new cobalt HSS bit from bunnies and drilled it myself. Bench vice, hard hit the target spot with something pointy to make a dent (was probably a stainless screw) and drilled the hole by eye with my corded drill using some bike chain oil as lube. Wasn't perfect, but it was close enough that the holes lined up with the motor. I figured if I stuffed it up I could just drill the other end, or chop a bit off the end.

Go slow with moderate pressure, don't let the drill just spin on the spot - if it's not cutting go slower with more pressure. Shouldn't take more than 10 or 20 seconds... surprisingly easy.

 

[Engibeer]

195 MPa shear strength is for something like a 2xxx alloy in H6 temper. Cheaper 1xxx grades with no heat treatment are as low as 50 MPa.

He said he got the ally off Fleabay, didn't state the grade or temper. If you split the difference and assume ~100 MPa your factor of safety is about 1.5

Aluminium is also very notch sensitive, hence the comment about the hole.

Cheers, I'm only a Mining Engineer. Materials aren't my common knowledge base. Haven't done shear strength calcs since uni :chug:

 

[Lyrebird_Cycles]

BTW the trick to cutting austenitic grades of stainless (eg 300 series) is to slow the tool down and press really bloody hard: if the tool isn't squealing press harder. If the tool snaps you pressed too hard.

The problems with cutting SS occur because it work hardens ( = strain hardens) under the tool; a slow tip speed reduces the strain in the cutting zone and good depth of cut means the next pass of the tool cuts under the strained zone.

 

[Lyrebird_Cycles]

Cheers, I'm only a Mining Engineer. Materials aren't my common knowledge base. Haven't done shear strength calcs since uni :chug:

No worries, I started out in aero engineering and I now make bicycles, I spend a lot of time working with lightweight high strength materials.

 

[Engibeer]

I purchased some Aluminium 6060-T5 off ebay before all this was posted.

http://www.ebay.com.au/itm/Aluminium-Solid-Round-Select-Size-Between-10-25mmx300mm-Bar-Lathe-Rod-6060-T5-/122037288843?var=&hash=item1c69fd3f8b:m:m6xn0lDP5f4TvJvxmPvmbWA

I downloaded AS1664 and a table specifies a minimum shear strength of 83MPa (looking up the data for 6063 as per the below) http://aluminium.org.au/FAQRetrieve.aspx?ID=43828

The mechanical properties of alloys 6060-T5 and 6082-T5,T6 are not shown in the Australian Standard AS1664 (The Structural Use of Aluminium). What should I do?




The guaranteed minimum mechanical properties of 6060-T5 are the same as for the alloy 6063-T5. Therefore use the 6063-T5 data in AS1664 for alloy 6060-T5.

With regard to alloy 6082 it has a chemical composition which overlaps that of alloy 6351 and the guaranteed mechanical properties are essentially the same. Therefore use the 6351 data in AS1664 for alloy 6082.

 

[luggy]

Sounds like you have the same coupler as me engibeer, I just took my coupler into a local fitter and turner and got a shaft with keyway and key made up for around $30

 

[Ducatiboy stu]

It's a grain mill, not a top fueler driveline!

One of these should just be able to cope

 

[fishingbrad]

Don't think so Stu. Those uni joints don't look like they can take the power of the MD Motor.

 

[Ducatiboy stu]

Don't think so Stu. Those uni joints don't look like they can take the power of the MD Motor.

As long as the mill doesn't jam it should be ok

 

[Engibeer]

Sounds like you have the same coupler as me engibeer, I just took my coupler into a local fitter and turner and got a shaft with keyway and key made up for around $30

Cheers,

Might do that if my aluminium bar shears!

 

[Weizguy]

Could someone tell me if this is what I need to connect a md motor to a minimill. 12mm to 1/2inch. Just want to make sure as it's pricey. Is there a cheaper place to get one? Or is this good quality? Cheers

https://www.ebay.com.au/itm/231704332567

Spider coupler

3 pc pack CNC Helical coupler

 

[zwitter]

Hi Les the wise guy

See post 655 pne page back. The ebay one is. 1/3 the price and does the job no worries.

James
Zwitter


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