Is Metal Magura Backings As Good As Cnc Backings.

[dave33]

CNC machining means enhanced accuracy and repeatability compared to a hand machined version.

CNC machining may not be the cheapest choice for mass production (each item has a relatively long cycle time, many minutes compared to seconds for a moulded item), hence the common choice of die-casting (the initial tooling cost upfront can be shown to be a minimal part of the unit cost if considered across the life of this tool) followed by only CNCing the important features like threads and faces requiring a high surface finish and accuracy of position.

A 100% CNC machined item may not be necessary for all fabricated items, but for highly stressed components / high quality finish components, then it is desirable.

Steve

just becasue its cnc'd dont mean its going to more accurate at all, repeatability yes defo

and as for accuracy, grinding and honing is how to produce this,

cnc is a brand almost these days.....

[Luke Rainbird]

just becasue its cnc'd dont mean its going to more accurate at all

What ARE you on about?

A CNC machine will kick out whatever you put into it, again and again to whatever precision the machine will go to (often as accurately as 0.0001" or more)

[TrashZen]

Right,

so when the rubber pops out of the metal backings, what glue do you use to put them back? Regular superglue, the araldite one that sticks in seconds?

(this just happened to my heatsink ones, both at the same time, though they operated trouble-free for nearly a year.)

By the way, on average, how long do you keep your pads for on SMOOTH RIMS? or until what level of rubber left do you keep them running?

Edited August 30, 2007 by TrashZen

[dave85]

What ARE you on about?

A CNC machine will kick out whatever you put into it, again and again to whatever precision the machine will go to (often as accurately as 0.0001" or more)

That's repeatability, not precision, they can be uniformly crap. Precision is expensive, and difficult to achieve at speed. Look at some of the older echo control boosters and you'll see where the cutter was deflecting because it was being pushed too hard.

[Tommy d]

By the way, on average, how long do you keep your pads for on SMOOTH RIMS? or until what level of rubber left do you keep them running?

After 3 years, my kool stop reds are about half worn down. Presumably softer pads would have a shorter life though...

[Heatsink]

Right,

so when the rubber pops out of the metal backings, what glue do you use to put them back? Regular superglue, the araldite one that sticks in seconds?

You can get good results with both glue types. Depending on the current shape of the pads, superglue is great for minimal gaps (actually stronger the thinner it is) and Epoxy resin (of which Araldite is a brand name) is a great gap filler. In the case of alu backings, the glue has less of a challenge to contend with. This is fortunate because inherently an alu to pad bond is harder to achieve than a pad to plastic backing one. Glues are strong in shear but weak in peal. A flexing plastic backing creates the tearing mechanism, wheras the rigid aly version sidesteps this.

That's repeatability, not precision, they can be uniformly crap. Precision is expensive, and difficult to achieve at speed. Look at some of the older echo control boosters and you'll see where the cutter was deflecting because it was being pushed too hard.

Edds right. With time being money (and a typical UK rate for machining £30 an hour with VAT to be added), you will see examples with rushed machining producing a poor surface finish as the tool is forced to move faster than it would like. Done properly with acceptable feedrates then all is good.

After 3 years, my kool stop reds are about half worn down. Presumably softer pads would have a shorter life though...

Actually, softer pad material can mean better abrasive resistance, although because of the floating magura pad holder design, when used on rims softer pads can mean increased deflection of the pad such that the area actually in contact with the rim dissapating all the wheel's energy is going to be smaller, and so this can lead to faster wear due to the increased contact pressure, and of course wear at angles where a pad is disposed of quicker since it has worn at too much of an angle.

Steve

[Greetings]

I'm sure you know best what you're talking about Steve, but surely CNC'd brake pads won't be any better than forged or cast ones. After all, even plastic is good enough for brake pads, you don't need anything super strong for that purpose. I value the quality of my Coustsinks and will never change them to any other pads but this whole "argument" started when somebody stated that CNC isn't necessarily better for brake pads?

[Tommy d]

Actually, softer pad material can mean better abrasive resistance, although because of the floating magura pad holder design, when used on rims softer pads can mean increased deflection of the pad such that the area actually in contact with the rim dissapating all the wheel's energy is going to be smaller, and so this can lead to faster wear due to the increased contact pressure, and of course wear at angles where a pad is disposed of quicker since it has worn at too much of an angle.

Steve

Do you think you could dumb that down a bit for me? I've read it through about 5 times and I still don't think I get it!

Are you saying that softer pad material means more friction, or that it is better at not being worn away? And is the next bit about pads being squashed and therefore not wearing evenly? Or have I got the wrong end of the stick?

Sorry, village idiot here, believe it or not I got an A in Physics A level... true story...

[Krisboats]

I'm sure you know best what you're talking about Steve, but surely CNC'd brake pads won't be any better than forged or cast ones. After all, even plastic is good enough for brake pads, you don't need anything super strong for that purpose. I value the quality of my Coustsinks and will never change them to any other pads but this whole "argument" started when somebody stated that CNC isn't necessarily better for brake pads?

I put some rockpad blue material into some plastic backings and the pads weren't good at all, they didn't hold, didn't bite... they were awful. Upon looking closely you could see the plastic backing flex at the edges as the middle of the backing was compressed in more. I decided to stick the material in my heatsink cnc backings and ta'daa!!!! fantastic working brake with and insane amount of noise.

[Heatsink]

I'm sure you know best what you're talking about Steve, but surely CNC'd brake pads won't be any better than forged or cast ones. After all, even plastic is good enough for brake pads, you don't need anything super strong for that purpose. I value the quality of my Coustsinks and will never change them to any other pads but this whole "argument" started when somebody stated that CNC isn't necessarily better for brake pads?

Hi Inur! Good point there. I would say though that I believe that there have been instances of plastic pad backings and cast aluminium backings breaking into pieces from the rigours of Trials use, but I've never heard of any Heatsink CNC aluminium backings breaking yet.

Do you think you could dumb that down a bit for me? I've read it through about 5 times and I still don't think I get it!

Are you saying that softer pad material means more friction, or that it is better at not being worn away? And is the next bit about pads being squashed and therefore not wearing evenly? Or have I got the wrong end of the stick?

Sorry, village idiot here, believe it or not I got an A in Physics A level... true story...

It was a hastily typed paragraph since I'm at work and shouldn't be surfing! No probs to simplify.

Basically, if you look at the data charts for pad material, they give data for a given compound in various hardnesses. They have a standard abrasion test which measures how much material was worn off in a certain test set-up. The data shows that the softer versions show a modest decrease in material lost during this test. The key thing is that this abrasion test is very different to how the pad is actually used.

When used as a magura brake pad then the softness actually kicks in effects due to the pads being held in a floating arrangement for Maguras (Vees are relatively rigid in how they're held). With this floating arrangement he brake surface of the pad distorts more which means a smaller portion may take the concentrated load. The higher the contact pressure the faster the wear rate, Force/Area, so smaller area, same brake force applied, higher contact pressure. I'm sure that I could better explain this, but hopefully this time it's a bit clearer!

As rule for a given pad type, the softer it is, the higher the coefficient of friction.

Please remember though that the typical band of hardness for brake pads is quite narrow, between 80 and 90ShoreA. We can see that in practice a wide range of compounds in various softnesses in this range give performance and life that riders are satisfied with.

Steve

[Balman]

i have done the oposite the backings on the rims jams snap caliper pistons how ever i loved the grip it had so i now have rim jam matirial in plastic backings and didnt bother with the metal backing as i had cracked bits off and it didnt sit in the caliper properly. If you are not geting on with the matirial id sugest new pads but these backings will die eventully so i personaly wouldnt bother how ever heatsink backings seem to be working really well so if your going to put compound in anything put it in there or plastic but rim jam matirial is really awsome gives off a really nice bite.

hope this helps

Jack