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mini mill motor upgrade?

Brian H

Brian H

Super User
I have a Princess Auto mini mill that has a 350w DC motor and would like to upgrade it to a 500w(possibly even brushless). Has anyone done this? My google skills obviously suck cause I can't seem to make heads or tails of a compatible (read swap out easily) motor replacement. I feel a bit intimidated to just buy something and hope I can make it work.
I have upgraded to a gas shock on the Z axis and installed a reverse switch so far. I watched the Frank Hoose (mini-lathe.com) videos on adjusting gibs etc. and have it working very smoothly. However, when I try and drill a hole bigger than 1/4" in anything the cutout/safety switch cuts the motor out. I assume this is to protect the delicate plastic gears inside.
I haven't had any issues with milling or fly-cutting tho
Any suggestions?
 
Im looking at a treadmill motor and matching speed controller, and adding a digital speed display, but ill be using the belt drive i have already upgraded to, which is somewhat better than gears but still i struggle with drilling over 1/2” in steel. The tread mill stuff is in around 1-2hp and still 110v
 
There are a couple you tube videos on doing that, it seemed to be a little more involved than I'm prepared to go right now, and, I'm a bit OCD with fit and finish of the final product.
Having that kind of power is intriguing, however, till my lathe gets here and I could make pulleys, etc I don't think the plastic gears would hold up.
I'd like to see pictures when your done tho
 
Ive put a DC treadmjill motor on a few tools with suitably rated AC voltage regulator and rectifier for speed control, They worked well for me.
I have a 4hp and 3.8hp for surfsce grinder and horizontal mill builds.
 
I'm not sure what your specific mill is but do some searching on its gears. If they are nylon/plastic then adding more power will only get you as far as the strength of the gear. Link below as generic example. All went well until he started putting load on it.

Its not clear to me if nylon gears are there intentionally to be the *inexpensive* sacrificial part to replace, or if its a production cost thing, or running noise thing... But seems like a common theme with lighter duty offshore mills & lathes. Some guys swap out the gear with metal if that's feasible & get a bit more performance. Anyways, try & Google your model or clone name equivalent because there is probably someone who went down this path.

post #86
https://www.homemodelenginemachinist.com/threads/cx601-milling-machine.24632/page-5#post-329375
 
This is a bit strange. 1/4 inch drill is small. Even 3/8 is not that big as far as energy needed to drill. 350w motor even with some power losses due to plastic gears etc. should deliver about 1/3hp to the actual work piece. Even if it delivers 1/4hp that should be enough to in theory with a sharp tool to remove 1/4 cubic inch per minute. That is around 4 cubic cm of steel (mild). This means with sharp bit you should be able to drill 4cm deep in 1min 1/2 inch hole. Not that bad.

Many years ago I had a mini mill with the brushless motor and I was able to drill 1/2 without any issues - the mill made excellent small drill press - about the only thing it was good for.

Note that this is with "sharp" HSS bits. As in brand new quality bits. In mild steel. I.e. ideal conditions.

Remember many drill presses that are older have 1/2 hp motors in them and they do 1/2 inch drilling without a huge problem with slower feed, cutting oil and some sharp bits. Old BP mills frequently had just 1hp 3ph motors - later on went to 2hp. Now smaller R8 have 3hp and larger 40 taper have 5hp - I think the 3hp is at the limit of R8 taper design.
 
Up a few posts from the link he says: during heavy drilling with a 1" diameter drill, in lo speed the selector knob jumped out of gear....
But jumped out of gear ended up being smearing the teeth off. He doesn't say his feed rate or if full drill diameter etc. but either way the gear was the limiting factor, not the motor power. I'm just saying check around a bit on the specific machine & see if ts been done successfully or maybe other upgrades at the same time.
 
There is huge difference drilling 3/8 and drilling 1". I also think the motor is not an issue - maybe the fuse system is.
 
Tom Kitta said:
Remember many drill presses that are older have 1/2 hp motors in them and they do 1/2 inch drilling without a huge problem with slower feed, cutting oil and some sharp bits. Old BP mills frequently had just 1hp 3ph motors - later on went to 2hp. Now smaller R8 have 3hp and larger 40 taper have 5hp - I think the 3hp is at the limit of R8 taper design.
Click to expand...

That's a good point. Drill presses usually always have belt drive system between the motor & spindle vs a gear box. So if overloaded, the belt slips or motor breaker goes, nothing expensive goes poof. Bigger mills have more power but no plastic gears in the head. So the mini mill is kind of a hybrid, lower power but direct gear drive. This makes me almost think the plastic gear (vs metal) is by design. If the machine is overloaded, the gear becomes the sacrificial thing that fails. Not a super easy replacement looking at the knockdown pics but its do-able & maybe better than taking out the drive train?
 
Plastic gears when well designed are strong enough to work for years - many years and preform at peak motor power. Arboga gearhead drill press (Sweden) uses plastic gears and metal gears. I have one that has like 40 years... works great. https://bbs.homeshopmachinist.net/forum/general/47332-weekend-tool-gloat-arboga-gearhead-drill

In case of mini mill I think its cheapness of the design - remember that the mill probably costs around 250 CAD at factory door - and factory needs a profit form that. There are kits available (as far as I remember) to change to metal gears. New plastic gears are quite cheap to buy as well.
 
In my case, the belt drive conversion slips under heavy load and I had converted to belt drive because my plastic gear exploded so I’m looking to go back to metal change gears which will also lower the overall height of my machine with long travel kit
 
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