Thread: Homebrew Slotter project !

Just came across this thread Baron, nice work and a great project. Keep it going!

Originally Posted by StrayAlien

Just came across this thread Baron, nice work and a great project. Keep it going!

Hi Greg,

Thank you for the vote of confidence.

At the moment work has ceased due to me managing to burn the mill motor out ! Only this time I'm not going to be able to repair it. The armature has well and truly cooked itself. I thought I was doing well having only had to replace the carbon brushes for the fourth or fifth time.

At the moment it looks like a new motor, whether it is a new PM DC one or a belt conversion, I don't know yet. Either way the job is stopped, for now anyway.

mate ... hop to it.

I have say, it made be laugh that your very first post in this 'projects' thread was a question to the assembled (enthusiastic) masses as to whether you should undertake a very cool machine building project or not.

he heh ... did you get any 'no's. . You committed yourself on that one! Love it. I know these things take time and a lot of priority shuffling / expense / apologies-to-SWMBO / gin / tonic / etc, but we're here to keep you going!

Hi Greg,

Many thanks for your post ! It's nice to have some encouragement, but it is a project that I had already decided to attempt, particularly since I have almost all the materials that I need.

Anyway back to the motor issue ! I have three salvaged treadmill motors, all of them different makes and power ratings, from 600 watts to 1000 watts. The big 1Kw one would be favourite, but its very heavy in comparison to the original motor. It also has a 3/4" inch diameter spindle, much larger than the original one.

So the 600 watt motor looks to be the the easiest to modify even though its 150 watts smaller in power rating than the original motor.

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These are the three motors that I have. All of them rotate in the wrong direction according to the wiring colours, but that is easily taken care of by reversing the supply voltage. Which is good because non of them have "reaction" brush gear.

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The first motor in these three pictures looks to be the most easily adaptable.

The shaft is a little bit larger in diameter than the original and doesn't have a keyway, which provides me with a choice of turning the spindle down to suit or boring the old gear out to suit the shaft. Boring the original gear is favourite, but I don't have a mill to cut a keyway in the motor spindle. Catch 22 !

I'll take some more pictures as I go along !

Thanks Guys:

Is turning a taper an option, my friend in highschool had a Sun autocycle with a Villiers engine, the flywheel was secured by taper alone, it never came loose.

Hi John,

I don't know the layout of your machine but would it be possible possible to fit a small 3 phase motor with VFD for a more reliable drive system? From what I have read online these treadmill type motor are not really suitable for machine tool use. If you get a 3 phase motor you could then use a standard Taperlock bush, after modifying the pulley of course.

Hi John, I don't know the layout of your machine but  would it be possible possible to fit a small 3 phase motor with VFD for a more reliable drive system? From what I have read online these treadmill type motor are not really suitable for machine tool use. If you get a 3 phase motor you could then use a standard Taperlock bush, after modifying the pulley of course.

Hi Lex, Guys,

Whilst I agree with you a small three phase motor and VFD along with a belt drive conversion would be one way to go !

The only real downside of using permanent magnet DC motors, ie treadmill motors isn't controllability, but heat ! The way these motors are constructed means that the only way for the heat in the armature to escape is through the bearings at the ends and good airflow down the outside of the armature. However having a good flow of air down between the armature and the field magnets does little when the armature is spinning. The flow of air is pushed away from the armature creating a skin effect reducing any heat being transferred to the air and removed.

You may also have noticed that many of these treadmill motors don't have any ventilation holes in them, some have an external fan that blows air over the body of the motor which helps. Also some have what you would call a substantial flywheel, usually cast iron attached to the spindle, often running the driving belt. This large heavy flywheel also serves to absorb the heat conducted up the spindle and dissipate it into the air !

Hi Guys,

I hadn't realised that I had two 1.25 HP treadmill motors, so I've made the decision to use this one,

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It helped that it seemed to have had very little use, since it was very clean.

The first thing before dismantling the motor was to remove the four mm thick pressed steel mounting bracket from the motor. Fortunately it was held on to the motor body by two M10 bolts, surprisingly considering how thick the mounting bracket was the bolts were very short only 12 mm long with a split lock washer on them.

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The next thing after testing was removing the carbon brushes ! Again these showed almost no wear, and seem to be a common type since I have a spare pair of replacement ones obtained for DC alternator.

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The commutator is also very clean when I ran this motor up in both directions there was very little arcing at the brush leading edge. The motor label states 180 Volts, which is what was applied to the motor using the mill power supply turned up to full. The motor still turns even at 8 volts.

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This is a picture inside the motor end cap showing how the brush holders are connected with soldered on push on tags. The original motor didn't have the tags soldered in place and were loose on both the wires and spades. This of course allowed the connections to get hot and start to damage the brush holders. One of the original modifications that I made was to solder the connections.

This motor has a 17 mm diameter spindle. Much bigger than the thin 10 mm diameter of the original motor.

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This is the driving gear from the spindle of the old motor. It has a 4x4 mm key and keyway. There isn't enough meat left to bore out should I decide to go down that route. There would be barely enough metal left to support the teeth. So the only other way would be to turn down the new motor spindle, though I'm tempted to bore this gear out to 12 mm and only turn enough of the 17 mm spindle down to 12 mm to get the gear into the right position on the shaft.

More later.

Hi Guys,

Not got much done today. I spent some time setting up the lathe with soft jaws in order to bore out the driving gear. I was going to enlarge it to 12 mm but the nearest plug gauge that I had was 13 mm -2 thou, so I used that. It should give me a good fit on a 13 mm spindle. Not much of the keyway left but there is enough meat to get it a little deeper.

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This is a picture of the bored out gear.

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These are some pictures of the disassembled motor. I need to turn that 17 mm diameter spindle down to 13 mm diameter. Fortunately there is enough length for me to do that. The keyway in that shaft happens to be 4 mm wide and 4 mm deep, but after turning down there probably won't be any of it left.

More later. Thanks for looking.

Hi Guys,

Some more pictures and a little work done over yesterday and today.

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First a picture of the bored out gear placed on the old motor shaft. The difference between 10 and 13 mm showing the remaining part of the keyway in the gear. I might have to increase the keyway depth in the gear a couple of mm. Fortunately I still have the slotting tool that I originally made and used to key this gear. I also used the original motor mounting holes as a template for drilling the new motor mounting pad.

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These two pictures show the mill motor mounting with the slotted holes for setting the gear engagement. The new motor mounting pad is shown on the right. Its made from a scrap of 1/2" plate found in the scrap bin. I cut a 4 inch square piece and scribed from corner to corner in order to get a centre for a drilled 10 mm hole. Using the centre point and a compass I scribed a 42 mm circle to locate the points for drilling four 4.2 mm tapping size holes which were then tapped M5, as can be seen. The hole positions were checked using the original motor mounting plate and the old armature shaft as a locating pin.

02-01-2023-003.jpg

This is the new treadmill motor end plate. I intend to turn the ribs down so that I can create a rim and locate the new motor accurately on its new mounting pad. If you look just below the red arrow you will see the small amount that I will have to turn off in order to locate the mounting plate in the new pad. Also note that there aren't any holes for screws as yet, this motor was mounted on its side originally. Also it wasn't until I put it in the four jaw chuck that I found that the casting is about 2.5 mm off centre, so I'm going to have to centre it up using the bearing bore inside that hole.

More to come and more pictures.

Hi Guys,

Having put the alloy casting motor mounting plate in the lathe four jaw chuck, I discovered that I wasn't able to get at the bearing surface in order to centre the plate up. So needing to be able to get into the hole from the front, I modified an existing dial gauge to use as an indicator.

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Some of you may remember the modifications that I made to this dial gauge so that I could clear the chuck jaws. Well I needed to get access to the bearing surface to use as a reference. I had a brass headed pin on a 2.5 mm shaft. I drilled a 2.4 mm hole in the aluminium arm and made a plastic sleeve to set the distance of the pin and then super glued it into the hole that I had made in the arm.

The brass headed pin fits nicely into the hole resting on the bearing surface inside. I had to turn the dial gauge sideways so that it cleared the chuck jaws. Using this I was able to set the motor mounting plate to an accurate centre.

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Using a grooving toolbit I turned the motor mounting ribs down to 72 mm to create a step that I could use to reference the motor mounting plate in the new adaptor plate. Note that I skimmed the surface of the casting with reference to the face of the bearing housing. Its now within a thou or so of being the same thickness all the way round.

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This is the new motor mounting plate with a 47 mm diameter hole through it to suit the casting diameter holding the bearing. The next step is to turn a recess into this plate to suit the 72 mm ring of ribs on the motor casting. Those fixing holes are also on a 72 mm PCD would you believe !

Anyway that's all for now, I'll take some more pictures later as work progresses.
Thanks for looking !

Hi Guys,

Quite a busy day for me today, but I managed to get some more done on the new motor mounting plate.

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Turning a matching taper for the ribs wasn't as difficult as I expected. I first cut the 3 mm deep recess for the locating edge that I had machined on the alloy motor mounting plate. And then turned the angled section. Since I had already measured the angle of the ribs at 30 degrees it was a simple matter of turning the top slide to that angle. It was more awkward avoiding the top slide from hitting the work, requiring that the toolbit had a fair stick out from the tool holder.
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It actually fit quite nicely, not a tight fit but no play either.

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All that was needed was to drill and tap four M5 fastening holes and then using four 12 mm M5 Cheese head screws to secure the alloy plate and the new mounting plate together. The last picture shows the whole lot fastened to the motor mounting plate from the mill.

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These two pictures show how I propose to hold the armature in order to machine the shaft down to 13 mm diameter. I need to make a lathe dog in order to rotate the armature. Hopefully I will get to do that tomorrow. The white plastic thing is a spindle thread protector.

Thanks for looking ! Your encouragement is appreciated.

So you are not going to use a catch plate to drive between centers?

Originally Posted by kafie1980

So you are not going to use a catch plate to drive between centers?

Hi Kafie,

Thanks for your post:

Yes I'm going to use a catch plate ! The pictures of the between centres was part of investigating how I was going to achieve being able to turn the shaft down to 13 mm. At the moment I don't have a lathe dog to use, hence my comment that I would have to make one. I will post pictures of the lathe dog and the setup with the catch plate in use later.

A far greater problem is cutting a new keyway into the armature shaft ! That existing keyway is 5 mm wide and 3 mm deep. I'm fairly sure that it will disappear when I turn the shaft down to 13 mm. No great problem increasing the keyway depth in the gear, but not having the mill working means that I cannot use it to cut a keyway in the shaft, and I don't think that I would have enough clearance to do it in the lathe.