How to: Homemade transmission fan (dailup warning)

Reply

  #1  
Old 05-01-10, 02:29 PM
Member
Thread Starter
Join Date: May 2010
Location: USA
Posts: 300
How to: Homemade transmission fan (dailup warning)

I have about a 15-year old mower with a Spicer/Dana hydrostatic transaxle that has a busted fan. Hydrostatic transmissions are notoriously temperamental about overheating so I went to the local mower shop to order a replacement fan. To my shock, they're no longer made. This mower is dawg-slow when the transaxle is overheated (which is all the time when it has no fan) so here's what I came up with for a replacement.

I bought a sheet of HVAC sheet aluminum from Home Depot. Then drew the design for the fan on a sheet of notebook paper using a compass, protractor and straight edge. I cut out the design template, cut out the hole in the center where it mounts on the hub and taped it to the aluminum sheet. Then I punched a pilot hole everywhere I needed to drill and drilled holes where all the ends and corners of all the cuts were to be.

The holes are important because stresses concentrate at square corners and could lead to premature failure. They also made it harder to overshoot my stop point when I was cutting.

This is the aluminum with the template attached:



I'm no engineer so this is mostly an intuitive design. I SWAGed at the width of the spars, which are slightly offset from the four hub mounting holes to spread out the stresses. When I drew the template, I thought to use a 1/4" drill bit for all the corners but in the final design thought better of it and used a much smaller drill. The curly mark on each blade was to remind me that that line didn't get cut.

This is the backside, showing the arrangement of the holes:



Next, I cut the hole out in the middle with a 1 1/4" hole saw. The hole cutter puts a good bit of torque on the workpiece so I figured I'd better cut out the hole before the blades. The shaft it has to fit around is only 1 1/8" but 1 1/4" was as close as I could get.

Then I drew lines with a Sharpie between the holes as my cutting guidelines.



Next I cut out the blades with a dremmel tool and cutting wheels. It took about 10 wheels total. Then I dressed the cut edges with the dremmel tool and a grinding stone and bent the blades to about 30.

This is the finished fan:




This is the old fan next to the new:



The old fan pretty obviously is rurnt.

This is the new fan mounted on the hub and pulley:




I also put some gorilla tape around the outer perimeter to limit blood loss until I can get it installed. I'd have rather shown it mounted back on the transaxle but I'd left it out on the patio and we're having a major thunderstorm at the moment.

Will if flow enough air? Dunno but I'm fair certain it will push more air than the one I took off.
Will it be durable? Not being an engineer, I couldn't say but I hope so. I'll let you know when I find out.

Beyond the lack of cooling, the old fan did nothing to keep the fins on top of the hydro pump cleared off. If the new fan flows any air at all, it should help in that regard. Plus, it will provide some measure of shelter to block some of the debris that the old "fan" allowed to settle onto the pump.
 
Sponsored Links
  #2  
Old 05-01-10, 02:32 PM
Member
Thread Starter
Join Date: May 2010
Location: USA
Posts: 300
The OP was limited to eight images so I had to make an additional post.

This is everything I used to make my homemade fan:



aluminum HVAC sheet (from Home Depot)
sheet of paper
compass
protractor
straight edge
pen
scotch tape
sharpie
scratch awl (used as pilot hole punch)
hammer
sheetmetal shears
electric drill
hole saw
scrap hood to cut aluminum on
quick grip to hold aluminum in place on scrap wood
imitation dremmel tool
dremmel cutting wheels
dremmel grinding stone
gorilla tape
 
  #3  
Old 05-01-10, 02:55 PM
Member
Join Date: Nov 2007
Location: NE Okla
Posts: 432
That is very creative!!

Me? I would've used the Gorilla duct tape to wrap around the old one....
 
  #4  
Old 05-01-10, 03:05 PM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 5,503
Very ingenious! iI'm impressed.


My intuition suggest that the airflow will wind up bending the fins of your fan. I hope I'm wrong.

Also, had the part not been available, I think I would have shopped around for a mower shop that had an old one they would salvage for you. Your design work would have been outside my inclination to try.


Hope it works like a champ for you ---- you deserve it!
 
  #5  
Old 05-01-10, 06:01 PM
Member
Join Date: Feb 2010
Location: U.S.A.
Posts: 248
Being a Tool and Die Maker, I like the idea of making a "better" replacement.
Maybe a few years ago, I could have done as good a job as you did. Just something about making it yourself --"MIU"
 
  #6  
Old 05-01-10, 06:39 PM
Member
Thread Starter
Join Date: May 2010
Location: USA
Posts: 300
Originally Posted by SeattlePioneer View Post
...My intuition suggest that the airflow will wind up bending the fins of your fan. I hope I'm wrong....
Unfortunately, you're right. The upside of the thin aluminum was that it was easy to work. The downside (among others) is that the wind definitely will "close the flaps" a bit. The fan is in a very remote location but I'll have to try to observe it while running to see if they're closing too much. Simply bending to, say, 45 or even 60 might be better. Or I might have to mod it with some fashion of a "hold-open" to prevent them closing so much. If I knew how many RPMs it turns when in operation, I might be able to devise a test to see.

EDIT:
In my list of stuff, that should be "scrap wood", not scrap hood. I can't seem to edit that post to correct it.
 

Last edited by Fred_C_Dobbs; 05-01-10 at 07:08 PM.
  #7  
Old 05-02-10, 12:19 AM
cheese's Avatar
Forum Topic Moderator
Join Date: Jul 2001
Location: USA
Posts: 16,575
Looks like a suitable replacement, good job!

At full speed the fan will be somewhere around 3000 rpm. I don't know if it will flex or bend the flaps enough to create a problem. I sort of doubt it, but I can't tell how thick that aluminum really is. Looks like it's enough but barely.
 
  #8  
Old 05-02-10, 08:43 AM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 5,503
Just to put a number on the issue of how much stress the fan will need to resist----

Assuming the fan is 6" in diameter, or a 3" radius, the circumference of the fan would be about 28".

At 3000 RPM the end of the fan would rotate 84,780 inches per minute, or 7065 feet, which would be about 80 MPH.
 
  #9  
Old 05-05-10, 12:18 PM
Member
Thread Starter
Join Date: May 2010
Location: USA
Posts: 300
The rain finally stopped and I got the transaxle back into the mower. Here's the homemade fan, installed:





After thinking about the "bending" factor, I upped the angle to closer to 45 but that caused some contact with the cooling fins so I went back to the original angle.

Now if I can figure out where the rest of those springs and control arms are supposed to go, I can test it out.
 
  #10  
Old 05-06-10, 09:39 AM
bontai Joe's Avatar
Member
Join Date: Apr 2004
Location: Pennsylvania
Posts: 592
I am truly impressed with your fan design, very nice. I never would have thought to leave the outer ring like you did, which should add strength to the over all design.
 
  #11  
Old 05-06-10, 10:38 AM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 5,503
I recalculated the edge speed of the fan to correct some errors, and the revised speed came to 53 MPH.
 
  #12  
Old 05-29-10, 04:12 PM
Member
Thread Starter
Join Date: May 2010
Location: USA
Posts: 300
I've worked on so much on this mower, I can't say for sure what's revitalized it but now it runs and pulls great. It finally has more torque than traction and runs like an 18-horser should.

I was thinking it was slowing a bit as it got warm, which I thought might have been due to the transaxle overheating, so I staged a couple of standing start drag races when barely warmed up and again after an hour of operation. In either case, the time is 34 and a fraction seconds. And after about six hours of running time, the blades on my homemade fan don't appear to have moved.
 
  #13  
Old 05-29-10, 09:25 PM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 5,503
I'm glad my concerns proved exaggerated.

Congratulations on your success with your project!
 
Reply


Thread Tools
Search this Thread
Display Modes
Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -7. The time now is 04:45 AM.