Triumph Rat Motorcycle Forums banner

1 - 20 of 22 Posts

·
Registered
Joined
·
324 Posts
Discussion Starter #1
I'm thinking about getting a brake disc turned to remove what chrome is left and to true it. I've read that they should be ground only, not turned, is this correct?
 

·
Registered
Joined
·
1,051 Posts
Hi Woodsie,
It is difficult to turn the brake disc parallel on a traditional lathe. The side pressure imparted by turning the thin disc at large diameter makes it difficult to control accuracy and judder.

I know there are special brake lathes with twin cutters that machine both sides at once, I have not ever seen one of these used, or the results.

Traditionally brake discs are ground on a special flat bed grinder (Blanchard Grinder), with the stone mounted on a vertical shaft, and the disc spinning on a magnetic chuck.
Many machine shops have these.

You might find it cheaper to buy a new non chromed brake disc. They made two sizes of disc 250mm and 10" diameter there is only 4mm difference, but this can cause problems. There are two sizes of brake pads to suit the different disc Diameters

regards
Peg.
 

·
Registered
Joined
·
191 Posts
As Peg says there are brake disc lathes that the automotive industry use, it's very common. A bike disc possibly won't fit but nothing to lose in asking your local brake place.
 

·
Registered
Joined
·
324 Posts
Discussion Starter #5
So it sounds like blancard grinding is the way to go. I'll see if there's anyone local that can to this and if not, I'll contact DBR, thanks for the contact Paul and thanks for all the input.
 

·
Registered
Joined
·
324 Posts
Discussion Starter #6
I'm also going to see what's available to buy. How to you edit a post on this site now?
 

·
Registered
Joined
·
1,051 Posts
Hi Woodsie,
There are three little Android style dots next to how long ago the post was uploaded, if you activate these ‘edit post’ should be on a pop up list.
Regards
Peg.
 

·
Moderator
Joined
·
6,522 Posts
Hi Thomas,

Ime, only partially-chromed discs need 'dechroming'; if the (original hard-) chrome is still complete on both surfaces, braking will still be good, even in the wet. It's when patches of chrome are missing that wet-braking particularly goes to pot. :(

I've read that they should be ground only, not turned,
Had all my Triumphs' original discs turned to remove remaining chrome, no problem. The engineers/machinists that did them were all aware of the requirement for both surfaces to be true to the inner mounting face and to each other, and they were/are so.

(Your T160's?) discs being chromed, they're likely original; if so, they'll have a 45-degree chamfer on each outer 'corner' between a braking surface and the edge of the disc. While not super-accurately applied - ime, the distance between 'em across the edge of a disc varies between 3/16" and 1/4" - they're an original disc's wear indicators. If they're present, make whomever does whatever machining you choose aware of this so they can advise whether the disc is worth machining - you wouldn't be the first person to receive beautifully-machined but wafer-thin discs ... :oops:

Risking stating the obvious, discs are heavy so, if you have to send 'em anywhere for machining, the total cost can easily exceed the cost of new discs? One of the reasons I had discs turned at various times was the engineer or machinist was nearby (end of the road or across a field in two cases :)).

If it becomes wiser to buy new discs, be aware they'll be 250 mm. OD, not 10" (254 mm.); there are pads with the braking material reduced by 2 mm. relative to the mounting holes for these discs.

Hth.

Regards,
 

·
Registered
Joined
·
5,216 Posts
I used Disc Brake Reconditioners to Blanchard grind (and drill) at least 20 discs over the years. 100% satisfaction and BEAUTIFUL work.

DBR
Disc Brake Reconditioners
618-344-7683
Caseyville,Illinois
Can't make any comment on the particular shop listed but last shop I worked at was owned /run by an old machinist. He ground all discs including floaters.

K
 

·
Premium Member
Joined
·
13 Posts
Fortunately I work in an engineering factory so I ground my discs. Turning will give you a result but the finish will not be as good as grinding and keeping the disc FLAT and PARALLEL is easier on a surface grinder. The surface grinding table is magnetic so it ensures the disc is held flat and minimises any vibration. Depending how worn the disc is, it may need to be turned over a couple of times. It's also easier to remove a few microns with grinding so more likely to keep the disc in spec.
 

·
Registered
Joined
·
1,739 Posts
I'm thinking about getting a brake disc turned to remove what chrome is left and to true it. I've read that they should be ground only, not turned, is this correct?
Hi Woodsie.

I took my T140 discs to a regular brake service centre to have them skimmed.

They couldn't perform the skim as they indicated the chrome would wreck their disc skimming machine.

I then handed the discs to a chrome plating business where they performed the chrome plating process in reverse.
Instead of plating the discs, the process stripped all chrome from the surface via electrolysis.
The discs were returned to me with the plating completely removed.

I then returned the stripped discs to the brake service centre where they performed a regular disc skim to true the surfaces.
If you look on the edge of your discs there's an angled edge.
This tells you how much the discs can be skimmed before reaching their limit.

Please note, whether the shop skimmed or ground the surface, I don't know.
The main thing is, that in my case the chrome needed to be first removed.

My discs came up brilliantly and so far haven't rusted.


cheers

R R
 

·
Registered
Joined
·
26 Posts
You can't 'turn' a crossdrilled rotor, - It is an 'interrupted cut' - doesn't work.
It has to be ground.
I do them on my flywheel grinder - take the time - let it spark out. It comes out good.
 

·
Registered
Joined
·
26 Posts
Depending on the design of the rotor, - the set-up can be difficult - if not impossible.
Price of new rotors is not much, - look into simply replacing
.
 

·
Registered
Joined
·
191 Posts
Please note, whether the shop skimmed or ground the surface, I don't know.
The main thing is, that in my case the chrome needed to be first removed.
If they were going to grind, the chrome wouldn't matter. A local brake place only has a skimming machine. According to this tech bulletin you can machine a cross drilled rotor.
How to properly machine a slotted rotor
 

·
Registered
Joined
·
1,739 Posts
If they were going to grind, the chrome wouldn't matter. A local brake place only has a skimming machine. According to this tech bulletin you can machine a cross drilled rotor.
How to properly machine a slotted rotor
Thanks Flash.

I visited 2 brake places today.
Over here they use the skim process with a blade each side of the Rotor..
As 1973 - 1981 Triumph Disc Rotors aren't made of high tech materials the standard skim process is the most economical method.
Straight forward set up and skim.
I paid $25 a rotor for machining.

The Disc Skimming machine operator I spoke to said he attaches the rotor on the machine and pushes 2 skimming blades against the rotor, each against each side of the disc.
After the first pass the blades are adjusted 2 thou in and a second pass is performed in the opposite direction.
If Rotors are in particularly bad condition further passes are done depending on serviceable thickness.

How much would grind process come too?

cheers

R R
 

·
Registered
Joined
·
324 Posts
Discussion Starter #18
TrueDisc, via Chicos link, charges $45. to grind a rotor. Paul, DBR appears to have shut their doors. A machine shop in the nearest big city said the can do but choose not to. Two local auto brake repair shops that I contacted don't do them. Another auto brake place said bring it in and they'll take a look. I'm doing that today. Apparently some auto shops turn them while still on the vehicle.
I know that we're not talking alot of money which ever way I go but I replaced a disc with an aftermarket one a few years ago, which has worked fine, but I can't bring myself to throw the old one away so if I this original disc gets sorted I will get my other bikes two discs done.
 
1 - 20 of 22 Posts
Top