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Re: (ET) Mower motor failure and blade balance
Hi,
This is true. I brought up the balancer as it can reduce vibration - even
with a new motor and blade.
I straightened mine with a straight edge, arbor press, V-blocks, dial
indicator, and lathe for final inspection. Here are the rough steps I
took.
Use a straight edge to see if the bend had taken place in windings part of
the armature. I think that it would be rare but its a quick check. Hold
the straight edge on the winding parallel to the axis of the shaft and
repeat every 45 degrees. I assume that bends are typically between the
large bearing and the windings because the shaft may be necked down in
that area for the windings themselves. The steps listed are based on that
assumption.
Arbor press
Having some V-blocks makes the straightening and checking process, easier
and safer but some plain blocking would do in a pinch. Note that checking
runout will be difficult with plain flat blocks since the armature will
move in relation to the indicator.
Use the blocks to support the armature at the bearing locations. The bend
occurred while the armature was supported at the bearing locations so the
straightening will be done under the same conditions. I would leave the
bearings on at this point to protect the shafts from getting nicked or
flat spotted.
Shim the small diameter end block so the armature is parallel to the press
table
Position a dial indicator under and near the end of the output shaft. Note
the runout and set the indicator zero to split the difference. For
example; a .010” runout should read +.005 to -.005
Rotate the armature so that the high spot is down. (Pressing the shaft
center will raise the end)
Place a large block, one long enough to cover the laminates of the
windings, and position armature so the ram is near the output end of the
windings. The ram needs to be over the windings. While pressing here is
not ideal, the motor may not have other areas that are accessible.
Activate the ram and press until the indicator reads zero.
Release the ram. Most likely the bend will spring back some. Use the
difference between indicator readings to determine how much spring back
there is and use that to get an idea of how much over shoot you need to
get to zero.
After each pressing, rotate the shaft to see if the high spot moved to a
different position. This could happen because of an over press.
Once things start looking good, also use the indicator to also check
output shaft runout near the bearing end. Check winding runout as well.
Repeat pressing and checking as necessary. I would think that if you get
the output to be within .002" runout would be awesome
Remove and discard the bearings. The balls may have been damaged during
the pressing. Its always a good idea to replace bearings when the motor is
apart anyway. Its a cheap maintenance item.
Use the lathe for final inspection, if you have one. Deburr (especially
the threaded output end) and clean the centers in the ends of the armature
shaft.
Mount between centers in the lathe. Verify runout at the output shaft and
bearing locations (bearings removed).
Regards,
Dean Stuckmann
5432 County Road U
Newton, WI 53063-9624
920-901-2288
> On Apr 20, 2024, at 12:18 PM, metman glasgow-ky com wrote:
>
> Blade balance is definitely important, but don't overlook shaft
> straightness.
> Some years back I borrowed a straightening fixture/gizmo from a
> lawnmower repair buddy of mine and fabricated a plate that kinda
> simulated the bolt pattern of the typical vertical shaft rotary
> lawnmower engine. That allowed me to mount the fat motors in the same
> manner so that I could indicate and straighten if necessary.
> Now I have several armatures that need to be straightened, but that
> fellow has past away and no one knows what happened to that crankshaft
> straightening fixture. And so far I've been unable to locate any old
> lawnmower shops that still had that fixture/capability to straighten
> lawnmower crankshafts.
> Yes, Stens sells a new one on eBay for about $400, but......
>
> Mike Wallace
> Glasgow, KY
>
> On 2024/04/17 4:28 pm, Christopher Zach via Elec-trak wrote:
>>> In 43 years of ET mowing (averaging 2 acres a week for 6 months of the
>>> year) I can only recall a single magnet failure. I use (2) tall motor
>>> decks; one for my lawn and another for vineyards.
>> Makes sense. The tall thin motors have never had a magnet failure that
>> I have seen (I have several cores for those) the problem was always the
>> darn armature shorting somewhere and causing the motor to "cog".
>> I'll take a look at the blade balance, I will say I do have more
>> vibration than I should, but I think the bigger problem is whatever
>> they used for adhesive is just wearing out.
>> C
>>> I think the secret to my success is using a precision blade balancer.
>>> I use a MAG-1000 and it is amazing.
>>> https://www.magna-matic-direct.com/blade-balancers/
>>> <https://www.magna-matic-direct.com/blade-balancers/> The deck was
>>> much quieter and I have to believe it extends bearing life as well.
>>> Blade straightness can also be verified.
>>> You may wonder how sensitive it is. In one of their videos they placed
>>> a sliver of paper on a 24” blade and the balancer moved.
>>> I wanted to see if my old unit was still up to the task. So I did a
>>> quick test yesterday and a placed a 1” long piece of electrical tape
>>> on an ET blade tip. The tape made the balancer move! I’ve found that
>>> even brand new OEM blades can have their balance improved with this
>>> unit.
>>> Yes, it is expensive but a wise investment in the long run.
>>> Regards,
>>> Dean Stuckmann
>>> 5432 County Road U
>>> Newton, WI 53063-9624
>>> 920-901-2288
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