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OT-looking to gather ideas-how to support cantilevered load on horizontal shaft motor

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  • Willy
    replied
    I like your execution of an alignment sleeve, good thinking.
    Also the entire assembly of components just seems to follow a best practices approach.
    Not always easy to tame the "paint shaker with a spark plug" that Tecumsehs are known for but as you say one gets a good feeling after an hour of run time as to how much better it now behaves.

    Leave a comment:


  • Doozer
    replied
    Fair enough. --D

    Leave a comment:


  • rickyb
    replied
    Originally posted by Doozer View Post

    Beep beep beep, back it up a but.
    I am an engineer too, but you are getting ahead of yourself.
    Everything you said is probably true. Yes indeed.
    But step back and see the big picture.
    Single cylinder engine, lots of instantaneous torque pulsations,
    I have first hand experience with more than a few Tecumseh 8 and 10
    hp engines. They vibrate a lot. They break gas tank brackets regularly.
    Ever use a snow blower with one? Holy crap they vibrate a lot.
    You want to sound like an engineer, talk some about overhung load,
    and you would be closer to the root.
    But bolt stretch, not a factor here, or so small a contributor that it is
    really a distractor. Not ideal, but bigger sins are causing his failure.
    Don't give machinists an excuse to pick on engineers.

    --D
    Well Dooz, there is method to my madness. I was just working within the original constraints. Substantially improve on the 7 hour changeout without major mods. Fixing the fasteners would in my mind shift the failure mode. The next failure would be the aluminum casting but the fasteners wouldn’t fall apart. Thought that might be a big enough, simple enough bandaid that meets the original goal. Of course getting rid of the vibrating noodle and decoupling is the real cure. I think the OP has a nice final solution.

    Leave a comment:


  • rickyb
    replied
    Originally posted by aribert View Post

    And that is what I did. I turned an alignment sleeve (started out as a piece of scrap 2 inch black pipe. ID was a loose slip fit, approx 0.060 wall, a slot the entire length of the part and a second slot opposite the first with a couple of narrow bridges remaining to hold the two halves together. Once aligned I spread the sleeve apart to remove.

    Some images attached. The welding of the pump mounting bracket is a bit of an embarrassment - I'm not a good welder to begin with but I used to be able to make a better looking weld with a stick welder. I'm not to concerned about the weld failing. Seems to work well after the first hour of use.

    rickyb:
    "I see a very typical capscrew fatigue failure caused by inadequate design. The problem is fasteners that are too short, are loosing tension then are fatigued to failure. Also the housing needs to be spotfaced under the screw head and a thick hardened washer added. Rather than a washer I would recommend a hardened spacer about 1” long and 1.25” in diameter to make up for the lack of stretch length in the capscrew. That will fix the problem...."

    I gave this post a bit of thought. I agree that using a spacer would allow for proper bolt stretch. I still think the failure is the cantilevered load under vibration. I'm not a Tecumseh fanboy but I seem to have two other similar sized Tecumseh engines and the fasteners that mount the engines to the other pieces of equipment simply fasten thru a 3/16 or 1/4 inch plate into the engine without the need of a spacer and the engines have not come loose in a couple of decades of very limited use. That said, I included 1 inch dia x 1 inch long spacers under the forward engine mounting holes - back two attachment holes are now directly under the axle and I did not have adequate room for such a spacer. I did torque the SHCS instead of just "good and tight" the first time.


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    I like your coupler solution

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  • Doozer
    replied
    Originally posted by rickyb View Post
    I see a very typical capscrew fatigue failure caused by inadequate design. The problem is fasteners that are too short, are loosing tension then are fatigued to failure. Also the housing needs to be spotfaced under the screw head and a thick hardened washer added. Rather than a washer I would recommend a hardened spacer about 1” long and 1.25” in diameter to make up for the lack of stretch length in the capscrew. That will fix the problem. You don’t need loctite. All it does is keep bolts from falling out, it does not prevent tension loss. If it makes you feel good use a light duty like 222.

    here is what is happening in the joint now. Typical fasteners stretch 0.004” per in of stretch length, yours is stretching maybe 0.002” as it is too short. The housing under the head yields during torque up and with some vibration relaxes and/or yields a little more. It only need to move 0.002” and bolt tension goes to -0-. This will happen almost immediately and may not need vibration to precipitate it. With no tension in the joint, it starts moving and failure of the capscrews is imminent. The washer reduces the stress on the housing material to well below yield and the spotface assures a well distributed stress pattern and can tolerate the stresses under the head of the screw.

    Relaxation is not just under the screw head but also on the back side of the flange and in the threads. Fastener stretch length is defined as the distance from the bottom of the head to the first engaged threads at the h
    Beep beep beep, back it up a but.
    I am an engineer too, but you are getting ahead of yourself.
    Everything you said is probably true. Yes indeed.
    But step back and see the big picture.
    Single cylinder engine, lots of instantaneous torque pulsations,
    I have first hand experience with more than a few Tecumseh 8 and 10
    hp engines. They vibrate a lot. They break gas tank brackets regularly.
    Ever use a snow blower with one? Holy crap they vibrate a lot.
    You want to sound like an engineer, talk some about overhung load,
    and you would be closer to the root.
    But bolt stretch, not a factor here, or so small a contributor that it is
    really a distractor. Not ideal, but bigger sins are causing his failure.
    Don't give machinists an excuse to pick on engineers.

    --D

    Leave a comment:


  • aribert
    replied
    Originally posted by [B
    Willy[/B];n2001493]
    This is my thinking as well, those old 8hp Tecumsehs do like to shake and with that much unsupported weight hanging out there something is bound to give sooner or later. I would solid mount the pump so that it does not act like a tuning fork, the Lovejoy coupling will compensate for slight misalignment and the spider will help quell vibration, that's what's so nice about that style of coupling. Having everything mounted rigidly will keep it all on the same page vibration wise, if it's going to shake at least keep it all on the same frequency......
    And that is what I did. I turned an alignment sleeve (started out as a piece of scrap 2 inch black pipe. ID was a loose slip fit, approx 0.060 wall, a slot the entire length of the part and a second slot opposite the first with a couple of narrow bridges remaining to hold the two halves together. Once aligned I spread the sleeve apart to remove.

    Some images attached. The welding of the pump mounting bracket is a bit of an embarrassment - I'm not a good welder to begin with but I used to be able to make a better looking weld with a stick welder. I'm not to concerned about the weld failing. Seems to work well after the first hour of use.

    rickyb:
    "I see a very typical capscrew fatigue failure caused by inadequate design. The problem is fasteners that are too short, are loosing tension then are fatigued to failure. Also the housing needs to be spotfaced under the screw head and a thick hardened washer added. Rather than a washer I would recommend a hardened spacer about 1” long and 1.25” in diameter to make up for the lack of stretch length in the capscrew. That will fix the problem...."

    I gave this post a bit of thought. I agree that using a spacer would allow for proper bolt stretch. I still think the failure is the cantilevered load under vibration. I'm not a Tecumseh fanboy but I seem to have two other similar sized Tecumseh engines and the fasteners that mount the engines to the other pieces of equipment simply fasten thru a 3/16 or 1/4 inch plate into the engine without the need of a spacer and the engines have not come loose in a couple of decades of very limited use. That said, I included 1 inch dia x 1 inch long spacers under the forward engine mounting holes - back two attachment holes are now directly under the axle and I did not have adequate room for such a spacer. I did torque the SHCS instead of just "good and tight" the first time.


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    Leave a comment:


  • rickyb
    replied
    I see a very typical capscrew fatigue failure caused by inadequate design. The problem is fasteners that are too short, are loosing tension then are fatigued to failure. Also the housing needs to be spotfaced under the screw head and a thick hardened washer added. Rather than a washer I would recommend a hardened spacer about 1” long and 1.25” in diameter to make up for the lack of stretch length in the capscrew. That will fix the problem. You don’t need loctite. All it does is keep bolts from falling out, it does not prevent tension loss. If it makes you feel good use a light duty like 222.

    here is what is happening in the joint now. Typical fasteners stretch 0.004” per in of stretch length, yours is stretching maybe 0.002” as it is too short. The housing under the head yields during torque up and with some vibration relaxes and/or yields a little more. It only need to move 0.002” and bolt tension goes to -0-. This will happen almost immediately and may not need vibration to precipitate it. With no tension in the joint, it starts moving and failure of the capscrews is imminent. The washer reduces the stress on the housing material to well below yield and the spotface assures a well distributed stress pattern and can tolerate the stresses under the head of the screw.

    Relaxation is not just under the screw head but also on the back side of the flange and in the threads. Fastener stretch length is defined as the distance from the bottom of the head to the first engaged threads at the h

    Leave a comment:


  • aribert
    replied
    Thank you all for your ideas.

    I think the most straight forward plan is to make a face mount bracket to hard mount the pump to the platform with the Lovejoy inbetween pump and motor - my cost is whatever scrap steel I use, some welding rod and a bit of mill time to square the bracket up. I could put a band clamp around the OD of the Lovejoy for purposes of alignment to get the pump reasonably close to concentric to the motor shaft. Playing with the Lovejoy coupling in my hand, I perceive the coupling has more forgiveness in angular misalignment than concentric misalignment.

    Using a piece of hydraulic hose as a coupling, I would need to buy a foot of hose that had a 7/8 ID and machine a pair of compression couplings (not having looked for 7/8 ID hydraulic hose, I am guessing that might be a modest challenge). I would make a "splined" sleeve (bore the ID and turn the OD on the lathe then using the rotab on the mill to machine longitudinal grooves in the OD of the sleeve) for the pump motor shaft to bring it up to 7/8 OD. If I replaced the key in the motor shaft with a lower profile key that had a couple of longitudinal splines, would that give enough grip for the clamped hose to bite into?

    Reconfiguring the system for a belt, I first discounted the idea. Now I think it may have merit. Rumaging thru my pulley box, I have 2 pair of automotive serpentine pulleys. In the image the upper left pair of serpentine pulleys are cast iron with a meaty hub for the full thickness of the pulley. The pair on the lower left have a hub with a stamped pulley pressed on. On the right is a pair of cast iron pulleys for v-belt - the upper one is adjustable for diameter and the lower one I would cut off the second smaller pulley. For all of these I would need to sleeve the pulley for the pump (0.5 inch shaft dia) and bore the other one out for the 7/8 inch motor shaft. The Lovejoy coupling was on the original logsplitter configuration with the 5 hp motor and I bored/broached the motor side for the 8 hp motor. A couple of images of the motor / pump spaced apart if I were to go the belt route. My understanding is that most v-belts are for fractional hp transmission. Will a serpentine belt transmit 8 hp?

    Any follow thoughts on this? Again thanks for your ideas.

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  • Willy
    replied
    Originally posted by The Metal Butcher View Post
    The shaft isn't the problem here. It's the shakey engine. All that vibration out on the end, especially if it's at a resonate frequency of the system will break everything. I'd add some distance, hard mount the pump and stick a short driveshaft in. No guarantees that's the right fix, as I've never encountered that problem in life before.
    This is my thinking as well, those old 8hp Tecumsehs do like to shake and with that much unsupported weight hanging out there something is bound to give sooner or later.
    I would solid mount the pump so that it does not act like a tuning fork, the Lovejoy coupling will compensate for slight misalignment and the spider will help quell vibration, that's what's so nice about that style of coupling. Having everything mounted rigidly will keep it all on the same page vibration wise, if it's going to shake at least keep it all on the same frequency.

    Chain couplers work well too but I find they are a little less forgiving than the Lovejoy style since they lack that elastomer spider that helps to dampen vibration while compensating for misalignment.I think they are even available in different durometer ratings.
    I actually have some of those hose style couplers. The ones I have are internal hex style drives with a locking collar on each end as used between motor and pump drives on large industrial furnace oil pumps, have used them on a number of projects.

    On my own splitter I went to belt drive since I had the room, it does eliminate a lot of issues.

    Leave a comment:


  • Doozer
    replied
    Aw that is a great idea ! ! !
    Sweet ! ! !
    I need to use this some time
    in my life on a machine.
    Thanks.

    -D

    Leave a comment:


  • Noitoen
    replied
    Originally posted by Doozer View Post

    Hydraulic hose over spline shafts.
    Brilliant.
    Did they have sleeve compression crimps
    like typical hose ends or some other type
    of hose clamp ? ? ? Interesting.

    -D
    Something similar to this but longer with 3 screws on each side
    Climax Part 2C-200 Clamping Collar is made from mild steel with black oxide coating for corrosion resistance. Dimensions are 2 in. ID, 3 in. OD, 11/16 in. Width. It is effective on hard and soft shafts.

    Leave a comment:


  • Doozer
    replied
    Originally posted by Noitoen View Post
    ..... 20HP 3000 rpm motors. The coupling between the motor and shaft were a piece of steel reinforced 1,5 inch hydraulic hoses clamped to the shafts. The shafts had splines .....
    Hydraulic hose over spline shafts.
    Brilliant.
    Did they have sleeve compression crimps
    like typical hose ends or some other type
    of hose clamp ? ? ? Interesting.

    -D

    Leave a comment:


  • Noitoen
    replied
    A long time ago I used to assist a company that made cement building blocks and the vibrating table for the forming had two counter rotating eccentric shafts driven by two 20HP 3000 rpm motors. The coupling between the motor and shaft were a piece of steel reinforced 1,5 inch hydraulic hoses clamped to the shafts. The shafts had splines but these motors started and stopped every few seconds all day. The start was a direct start and the stop, almost instantaneous, line voltage rectified DC on two of the phase windings. These hoses insulated the vibration and lasted a long time.

    In your case, The engine and pump can be mounted separately and bridged by the hose and the original shaft key way would be enough.

    Leave a comment:


  • aribert
    replied
    Originally posted by true temper View Post
    Keep the love joy coupler get some good studs and locktite them in the engine. The bolts are breaking because they got loose. Now your threads in the aluminum motor are compromised.
    No - it was a pain to remove the broken off bolts as they were Loctited in place (permanent, red). I had to heat the joint so that I could remove the bolts with vice-grips. On one side I could only rotate the bolt about 60 deg before needing to get a new grip - only got 1 to 1.5 turns out before needing to reheat the joint since the aluminum conducted the heat away too fast.

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  • Captain K
    replied
    I would belt drive the pump. Propbably also add vibration isolators to engine mounting. A single 5L or B width belt would handle the load easily

    Leave a comment:

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