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Farmer John

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I have made many aluminum Friction Pulleys by destructive machining, and recently came across Shape Ways plastic pulley, made by the  constructive process, 3D printing,.....and for only $5.  I had to take a look at these.  The concentricity is good, but the hole for the motor shaft measures .265, and needs to be opened up to .275.  Also the roll pin hole, which measures .067, needs to be opened up to .086.  I wouldn't recommend enlarging the holes with a Black and Decker, or recommend using a twist drill in a drill press.  Not many folks will be willing to buy a $25 reamer to ream one hole in a $5 part.
     At the recent Wi/Il gathering, held by Mrs. D, Miriam was kind enough to leave five, yes, five distressed Elna machines for rehoming.  The Elna Transforma is the ideal platform  upon which to install the plastic pulley, since the Bakelite/rubber pulley on the Transforma has upon it three flats...the machine sounding like a jack hammer...REALLY.  The handwheel has been removed, the pulley roll pin removed, the base of the sm removed, and the roll pin removed from the horizontal knee bar.  All that remains is for me to withdraw the knee bar, reposition the motor to allow the pulley swap and reassemble.  I need three hands for this.  Stay tuned for the results.

Something has changed, I can no longer attach a photo

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Zorba

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Reply with quote  #2 
Very interested in this - hopefully your picture posting woes will cease soon!
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Miriam

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Reply with quote  #3 
John, I’m so glad those fine machines are now in good hands.
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Farmer John

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Reply with quote  #4 
Yes, Mariam, a couple Elna sm went 500 miles away, with me taking what was left over, ha, ha.  The trouble is that I can't stand to have a sm around here that is inoperative.....I have the burning urge to fix them, and I don't need more Elna's for myself.  Luckily, I already have a request for one of your Supermatic's from a sewing group member, so I have fun fixing one, and off it will go, "Pay it Forward".  Shall I get a Supermatic operating for return to you ??

I can't attach photos now, while I had no problems in the past.  My attempts result in an "Alert" dialog box, stating that the photo could not attach due to an HTTP error.  Someone please, HELP ME.......photo files are jpeg.  Neither "attach files" nor Insert Photos" will function.
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Zorba

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Reply with quote  #5 
Have you tried another browser? Push comes to shove, PM me for my email, I'll post 'em for ya.
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Farmer John

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Today, I swapped out the OEM friction pulley for the plastic Shape Ways pulley.  As I removed the kneebar, I was pushing it out with an 8 inch long 1/8 inch diameter steel rod, which I left in place.  The rod retains the washers that are on either side of the motor mount.  That slight difference in diameters gave enough movement to the motor to slide the old pulley off of the motor shaft and slide on the new one.  Sliding the knee bar back in place displaced the 1/8 inch rod.  Next was to replace the two roll pins, and screw on the base plate.  That 1/8 inch rod was my third hand to hold those washers in place.  The operation is easier to do than explain.  Winding a bobbin, threading the machine, and sewing a test piece with tension adjustments, completed the repair.
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Zorba

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Reply with quote  #7 
Photos from Farmer John:

Shape Ways friction Pulley, ready to install
100_1743.jpg 


OEM Pulley with large flat spot:
100_1744.jpg 


Line of stitches after assembly of machine:
100_1745.jpg 



New Friction pulley installed:
100_1746.jpg



Center of Photo - Drilled & tapped the end frame so that the motor can be pushed away from the friction pulley.
  100_1748.jpg 


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OurWorkbench

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Reply with quote  #8 
Thank you!!

Janey

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ArchaicArcane

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Chiming in late here - is there enough room that the Shapeways friction pulley could be printed a touch bigger?  I have a 3d printer now and found that when I printed the pulley from the same file that was uploaded to Shapeways that it was a touch smaller at all openings than it should be (blue one) but if I printed it a 107% and all measurements seem close enough they shouldn't have to be drilled out but I haven't had time to test the fit yet to see if the pulley is too large now (silver one).

67094371_2377898992300208_815422493450829824_n.jpg   

The Elna yahoo group has a file about how to lower the motor for install of this pulley and another doc about the pulley that says the 2mm roll pin hole should be drilled out.  I can upload them if anyone is interested.  The group also has a 3d file for a roll pin removal tool.  That I have had a chance to try.  It's pretty slick!  It uses a 1/4 - 20 barrel nut and bolt and a cut down rivet pin and pushes the pin out with only a little more than hand pressure.  I plan to make a video on it when I get organized.

This is a pic from the Elna group:
Pin+Extractor-4.jpg 




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Farmer John

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Reply with quote  #10 
There is plenty room to accommodate a larger pulley.  See photos of sm above.
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ColoradoJim

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Reply with quote  #11 
That pin removal tool looks really slick and compact as well. I have one of the supermatics where there was not enough room to remove the pulley after the pin was tapped up. Rather than lower the motor my method was to remove the threads holding the base cover and then loosen the 4 remaining threads just enough where one pair farthest away from the pulley was loosed the least and the pair closest to the pulley loosened up enough so by angling the base there was enough clearance to pull the pulley out through the opening.

This solves the problem of possibly losing a thread inside the machine and not messing up any timing with the timing belt that would otherwise be in the way.

I wouldn’t mind seeing the method of lowering the motor though!
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ArchaicArcane

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Reply with quote  #12 
Quote:
Originally Posted by Farmer John
There is plenty room to accommodate a larger pulley.  See photos of sm above.
Farmer John


I guess what I was wondering is if the larger pulley will push the motor out of alignment a little. I can tell it will physically fit into the area but once the handwheel is installed will it be too tight / change the surface contact angle / etc or will that spring that holds the motor against the wheel just accommodate the increase in diameter.

I borrowed a Supermatic to test with on Friday and found that the motor needs to be lowered in order to remove/replace the pulley last night so haven’t been able to test that.

If it won’t fit, I can enlarge the holes in the file without enlarging the pulley - but it will take some effort in CAD which I’m still learning - then print.

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Farmer John

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Reply with quote  #13 
The motor has lots of movement upon its pivot point, (knee bar), and the spring that holds the motor against the hand wheel will accommodate  differences in pulley diameter.  Obviously since the motor pivots through an arc, the line contact between the hand wheel and the friction pulley would change a little with an increase in pulley diameter, but not enough to affect to contact of the "0" rings with the angled surface of the hand wheel.  Increasing pulley diameter would cause the upper "0"  ring to have less force against the hand wheel, which could be corrected by a change in the angle of the pulley's friction surfaces.  The change would be very minimal, and not worth doing the math.
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ArchaicArcane

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Reply with quote  #14 
Quote:
Originally Posted by ColoradoJim
That pin removal tool looks really slick and compact as well. I have one of the supermatics where there was not enough room to remove the pulley after the pin was tapped up. Rather than lower the motor my method was to remove the threads holding the base cover and then loosen the 4 remaining threads just enough where one pair farthest away from the pulley was loosed the least and the pair closest to the pulley loosened up enough so by angling the base there was enough clearance to pull the pulley out through the opening.

This solves the problem of possibly losing a thread inside the machine and not messing up any timing with the timing belt that would otherwise be in the way.

I wouldn’t mind seeing the method of lowering the motor though!



What you're describing sounds similar.  I was about to upload the file but then I realized it was over 5mb.  I will check with Steve to make sure that's OK.

This borrowed Supermatic I have here also has the clearance problem so that's why I went looking.  Lowering the motor wasn't high on my list of things to do but since it's borrowed, the suggestion of trimming some of the metal that was made in one of the documents on changing the pulley was 110% out of the question.

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ArchaicArcane

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Reply with quote  #15 
Quote:
Originally Posted by Farmer John
The motor has lots of movement upon its pivot point, (knee bar), and the spring that holds the motor against the hand wheel will accommodate  differences in pulley diameter.  Obviously since the motor pivots through an arc, the line contact between the hand wheel and the friction pulley would change a little with an increase in pulley diameter, but not enough to affect to contact of the "0" rings with the angled surface of the hand wheel.  Increasing pulley diameter would cause the upper "0"  ring to have less force against the hand wheel, which could be corrected by a change in the angle of the pulley's friction surfaces.  The change would be very minimal, and not worth doing the math.
Farmer John


I just looked back at my notes.  The 107% was bothering me because the 2 pulleys don't look that different in size.  

The roll pin extractor is printed at 107%. 
The friction pulley is at 101.56% (on my printer) - That's probably not even relevant as far as an OD change in this case. 

In a quick look, I didn't see if the Shapeways file could be printed x% larger or smaller (maybe that's available upon logging in?) Perhaps with your measurements - those who don't want to ream it out could specify a larger print.  The person who originally created the 3d print file said he had to print a little bigger on his printer to get the correct dimensions - larger than I did, it's possible the same is happening at Shapeways.

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