PCD Redrilling

[Niall]

Hi All,
I know redrilling a PCD into a disc is quite common but i was just wondering what about elongating the bolt holes? Basically I'm looking at some new discs which are 4x100mm and obviously i need 4x108mm. Is there any reason why i can't have a machine shop just elongate the holes? I can't see any reason why not as its only the clamping force between the wheel and hub and the centre bore that holds the disc where it should be?

[Jimbo]

Surely you would have the get the centre machined to right centre bore aswell?? Cant see a problem doing that though. Would it weaken the disc at all though

[C2K]

Only the machining op. It's easier just to drill a new hole on pillar drill than elongate with an end mill/slot drill.

[Toms306]

As its still 4 to 4 I'd just have them re-drilled in between. It's when you have to try and work 5 around 4 that becomes difficult lol.

[cully]

centre mark and re drill them yourself with new holes easy job if you have acsess to a good pilar drill

[Jonny81191]

As its still 4 to 4 I'd just have them re-drilled in between.  It's when you have to try and work 5 around 4 that becomes difficult lol.

^this TBH.

[Connor]

I've definitely seen it done in a vice and cordless drill wasn't me though

[insomaniac45]

being a machinist by trade, i would strongly dis-advise elongating the holes, you will create stress points. if you can, always drill into good solid sections, and as it has already been mentioned, drilling the new holes at 90 degree offset to the ones already there is the best option. As long as your good with a drill, there is no need for a pillar drill. A pillar drill only allows for almost perfect straightness, it does nothing for wobble or drift, which you may get on a normal hand drill .

Disks are normally made from cast iron, which is self lubricating as long as you dont overspeed the drill, or try and drill a too big hole from the get go. (by self lubricating, i mean for drilling and machining, if it is for a brake surface, we are not allowed to use oil based coolants, as the cast is porous and soaks like a sponge. The swarf is almost graphite in texture and it is this that self lubricates)

[highwayman306]

Yeah what insomniac said, and you're gonna need some decent drill bits too Niall

[allanallen]

being a machinist by trade, i would strongly dis-advise elongating the holes, you will create stress points. if you can, always drill into good solid sections, and as it has already been mentioned, drilling the new holes at 90 degree offset to the ones already there is the best option. As long as your good with a drill, there is no need for a pillar drill. A pillar drill only allows for almost perfect straightness, it does nothing for wobble or drift, which you may get on a normal hand drill .

Disks are normally made from cast iron, which is self lubricating as long as you dont overspeed the drill, or try and drill a too big hole from the get go. (by self lubricating, i mean for drilling and machining, if it is for a brake surface, we are not allowed to use oil based coolants, as the cast is porous and soaks like a sponge. The swarf is almost graphite in texture and it is this that self lubricates)

Could you explain what stress points elongating the holes would make?

I do not agree with your comments about the pillar drill at all, if you centre drill first, use a correctly sharpened drill and have the job fastened down positively you will have very little to no 'wobble' or 'drift', fantastically accurate in the right hands.

With the sizing not being critical on the bolt hole I would always centre drill and then drill straight out to size, no pilot hole as they can often cause more problems. I personally wouldn't attempt this with a pistol drill.

[C2K]

Or

being a machinist by trade, i would strongly dis-advise elongating the holes, you will create stress points.

Being a mechanical engineer by trade,  no it won't. A slot would work no differently to a hole under the effect of a rotational force perpendicular to the normal plane. It's not exactly a figure of 8.

There should be no interface to speak of when slotting correctly if that's what you infer. If that's the case, I'd find a better machinist. Drilling the holes 90 degrees out is fine, but I answered the question Niall asked.

Niall, it's easy to do either. Redrilling is plenty quick. I had 100 done during a Rover group buy.

[Niall]

Well guys, I'm not dead yet. The holes were elongated by my local machine shop very easily. I would also like to point out that the wheel bolts do nothing to stop the disc spinning under heavy braking. Its purely the clamping force between the hub and wheel which holds the disc in place so there will be no stress put on the bolt holes. At least there shouldn't be!

Now i just need to get them fitted.

[insomaniac45]

Could you explain what stress points elongating the holes would make?

I do not agree with your comments about the pillar drill at all, if you centre drill first, use a correctly sharpened drill and have the job fastened down positively you will have very little to no 'wobble' or 'drift', fantastically accurate in the right hands.

With the sizing not being critical on the bolt hole I would always centre drill and then drill straight out to size, no pilot hole as they can often cause more problems. I personally wouldn't attempt this with a pistol drill.

wtf. i did a whole reply.... and its gone

But. The stress points will be created at the flat spots that are created from elongating the holes.

And yes, a pillar drill in the right hands, is a very accurate machine. But a pistol drill in the same hands as some one who knows what they are doing can be just as accurate. i do agree, every hole really needs a centre drill first, as that alone helps prevent drift. But wobble is all done to how the drill is ground. I am not knocking peoples skills in any way.

I do have to apologize for jumping the gun, as the elongations are only 4mm a side, which is not a lot at all. I do have a terrible habit of over analyzing things, and making solutions over complicated.

But, you have done it now Niall, and i am sure it will be absolutely fine.


Tony.

[Rippthrough]

No real issue with elongating the brake disc holes tbh, drilling new ones is easier tbh, but mine had great big slots in 'em:

[allanallen]

Worlds shitest ash tray.... Well done Phil!

[insomaniac45]

those are nice disks.

Wavy, i bet they almost make the car endo.

[Rippthrough]

Worlds shitest ash tray.... Well done Phil!

They're even worse after 2 years on the shelf in a leaky garage

[allanallen]

Worlds shitest ash tray.... Well done Phil!

They're even worse after 2 years on the shelf in a leaky garage

Worlds rustiest door stop? 

[Rippthrough]

Think I might use them for book ends for my small magazine collection: