M310100K Springs for loading motors against the racks
 

The springs for loading the motors should have a tension of about 12kg [25 lbs] while extended to about 128mm [5"] between the centers of the eyes at the ends of the springs. None of these specs need to be very exact.

I had springs made in Cape Town by my regular springmaker who uses pre-hardened wire and manages to wind a very tight spring. His springs need quite a lot of force to start opening the coils - a lot of force is needed before anything moves. Springs which are heat-treated after shaping are a lot more "relaxed". The drawing showing 38 turns of 2mm wire around a 12mm mandrel is therefore only a guide for someone who is going to cold-form springs for you.

I would very strongly suggest that you buy a cheap fisherman's scale to check the actual motor spring tension. If necessary, the anchor point of the spring can be moved to make it tighter, ot the spring can be stretched to make it looser.

Regarding catalogue springs, the McMaster-Carr / 9654K324 looks like a good candidate.

Here is "spring shop" in Germany: www.federnshop.com Their Z-144I or RZ-147OI look like possibilities.

I've done business with these guys and found them to be very knowledgable and helpful:

http://www.centuryspring.com/

Dave

Thanks Dave. Their S-597 looks good.

Dimension help needed.
 

This post moved from elsewhere:

I'm having a brain malfunction. Can someone tell me the distance between spring connection points when in tension holding motors into the rack?

From the first post in this thread: "The springs for loading the motors should have a tension of about 12kg [25 lbs] while extended to about 128mm [5"] between the centers of the eyes at the ends of the springs. None of these specs need to be very exact."

Maybe someone else, with the same type of springs as you, could give you the dimension. What springs do you have?

It will also be influenced by the pinion diameter, thickness of d-sided tape, and height of the ground rail, but it isn't really that critical. The ballpark is 12kg [25 lbs] of tension.

I went out today to get some quotes for all of the nuts and bolts for my new MechMate. Anyway, while I was in the engineering place I happened to look over and I see a spring that looked very familiar. (I'm sure I've been looking at the MM drawings for too long) I thought I'd buy one just to see if it actually came close to the MM drawings.

How lucky was I... The spring is manufactured by Century Spring Corp (but I got it from Stone & Son at Nowra, in Aus) It has an OD of 15.875mm (5/8"), 82.55mm (3-1/4") long and wire thickness of 1.829mm (0.072"). It has 35 turns... I was feeling even more lucky... Then I thought I'd test out the extended dimension under load. So I filled a jerry can with about 12 litres of water (I didn't have scales handy) and hung it from the spring. Under load it came to around 150mm. I'd say that's close enough.

If anyone in Aus is interested, I drive past this place most days and can pick them up and post them for you. At AUS$7.85 each, I think it's a massive score!!

Now that I've got the first part of my MM, I better get cracking on the rest.

ball park for springs
 

Hi, I see Gerald says spring tension is approximate, but could anyone give some sort of ball park of whats acceptable? My springs stretch to just over 110mm with 12Kg load - what are the dangers of too much tension?
Thanks, Jonny

no worries, a few kg won't break the motor shaft... & a lot more to break the tiniest bolt...

Ok good, just wanted to make sure. Thanks Ken.

Great site, thanks for sharing.

For any Aussies looking for springs, I found the same C-181 spring that Colin mentioned above at my local Bunnings for $4.98 each. Bargain!

For some reason you have to add the typenumber twice in there search function to find the ones you need. (Type it-enter, type it again, enter) before it shows the springs you are looking for. They asked reasonable shipping for foreign orders.