sonic Posted February 25, 2012 Report Share Posted February 25, 2012 Before I troll the internet does anyone on here do disc skimmimg?i have a pair from a gt750 I'm restoring that need a clean up. Would rather give the work to another forum user. Mark. Link to comment Share on other sites More sharing options...
kaighn80 Posted February 26, 2012 Report Share Posted February 26, 2012 whats the diameter of them, im sure someone here could put them on a lathe for you, i can do car ones because i have a machine that was built to do it, dont think it would do bike ones though. id be careful that it doesnt end up under the min thickness though. Link to comment Share on other sites More sharing options...
sonic Posted February 26, 2012 Author Report Share Posted February 26, 2012 They are 295mm with 56 centre bore.Min thickness not a prob as bike will be used minimally. Link to comment Share on other sites More sharing options...
kaighn80 Posted February 26, 2012 Report Share Posted February 26, 2012 i think a quick pm to kayla might be worth a shot, i'd say about doing it on my lathe but its past its best and the operator is crap. Link to comment Share on other sites More sharing options...
speedy sie Posted February 26, 2012 Report Share Posted February 26, 2012 disks should be surface ground not lathe skimmed... Link to comment Share on other sites More sharing options...
sonic Posted February 26, 2012 Author Report Share Posted February 26, 2012 I can get them ground locally if thats the case,Thanks. Link to comment Share on other sites More sharing options...
gixerboy1 Posted February 26, 2012 Report Share Posted February 26, 2012 disks should be surface ground not lathe skimmed... Why? Link to comment Share on other sites More sharing options...
speedy sie Posted February 26, 2012 Report Share Posted February 26, 2012 this is how they are done when they are made,the lathe can pick up on the drilled disks and the grove on the other types. Link to comment Share on other sites More sharing options...
sonic Posted February 26, 2012 Author Report Share Posted February 26, 2012 Mine are solid as they are from ancient times. Link to comment Share on other sites More sharing options...
gixerboy1 Posted February 26, 2012 Report Share Posted February 26, 2012 Just because something is comes from the factory like that, doesnt mean it is the best way of doing something, normally it means it is the cheapest. Considering the marks on a disc are radial, I would think they are not done on a surface grinder. Looks like the edge of the wheel is used not the flat. Not tried turning a stainless disc, only cast iron ones, but I have been told the best way is to have 2 cutting tools facing each other the gap between them set to what you want to turn the thickness to and then face the disc (using the bolt holes to secure the job, obviously you couldnt hold it in a chuck this way. Even pressure on both faces would stop the distortion. Link to comment Share on other sites More sharing options...
porter_jamie Posted February 26, 2012 Report Share Posted February 26, 2012 How much is a brand new disk? Link to comment Share on other sites More sharing options...
sonic Posted February 26, 2012 Author Report Share Posted February 26, 2012 .I'm trying to use as much of the original as possible.If not it's buy an old bike in bits and bolt it together rather than restore Link to comment Share on other sites More sharing options...
Superdunc Posted February 26, 2012 Report Share Posted February 26, 2012 All the race discs I've seen have had ground finish, so I'd say it's as good away as any to reface a warped disc. Unfortunatly the shape of many older discs doesn't lend it's self to surface ginding so the 2 tool method on a lathe with a fixture to hold them on th chuck is the way to go. Link to comment Share on other sites More sharing options...
gixerboy1 Posted February 26, 2012 Report Share Posted February 26, 2012 They are not surface ground, they are cylindrical ground. Link to comment Share on other sites More sharing options...
speedy sie Posted February 27, 2012 Report Share Posted February 27, 2012 They are not surface ground, they are cylindrical ground. cylindrical ground is surface grinding....this is wot i meant... Link to comment Share on other sites More sharing options...
gixerboy1 Posted February 27, 2012 Report Share Posted February 27, 2012 In the same way that milling is turning? Link to comment Share on other sites More sharing options...
eddie Posted March 3, 2012 Report Share Posted March 3, 2012 They maybe circular ground on a surface grinder.................. Are they warped, or just need cleaning up (ie rusty) If its just rust, coarse wet and dry with wd40 or paraffin would do. If theyre warped, youre probably looking at the 2 tool in the lathe job. Regards Paul Link to comment Share on other sites More sharing options...
lorenzo Posted March 3, 2012 Report Share Posted March 3, 2012 If they just need cleaning up a quick run round the block with a few applications of the brake'll sort it out, followed by a squirt of brake cleaner. Link to comment Share on other sites More sharing options...
speedy sie Posted March 3, 2012 Report Share Posted March 3, 2012 this is wot i ment. Link to comment Share on other sites More sharing options...
gixerboy1 Posted March 3, 2012 Report Share Posted March 3, 2012 They maybe circular ground on a surface grinder.................. Why would you do that? Its like using a rotary table on a mill to do a job that could be turned. Using the full face of a surface grinding wheel means the disc is more likely to push off and not be flat once it has been machined. As for the video, it is done by someone that has no knowledge of grinding or they would have known to turn the grinding wheel through 90 degrees and use the edge of the wheel to get them flat. Link to comment Share on other sites More sharing options...
eddie Posted March 4, 2012 Report Share Posted March 4, 2012 One of the places I used to work, had a "surface grinder". I think it was called a Lumbsden, summat like that. You mounted a number of abrasive blocks into a rotary head. The job was clamped to a magnetic table.The head turned and was passed over the job (left - right) like surace grinding, but gave a rotary pattern. This is what I meant by "rotary grinding on a surface grinder" Why would you do that? Its like using a rotary table on a mill to do a job that could be turned. You might not have a lathe? Ive used a CNC mill to do roundy jobs on, cos it was easier and quicker............... Link to comment Share on other sites More sharing options...
gixerboy1 Posted March 4, 2012 Report Share Posted March 4, 2012 Could you use a Lumsden grinder to do a disc? Only if it was a floating disc and you could remove the centre. The Lumsden you are describing sounds very rare, every one I have seen has a rotary table on it and as you do not have fine control on it you could not do a solid disc on the rotary. Look at the rotary pattern on any disc and it is easy to see it has been done around the centre of the disc. As for the lathe comment, the video showed a grinding wheel set on a bed of a lathe with the disc in the chuck, but if the grinding wheel was set at 90 degrees to what is shown you would cut on the front edge of the wheel and everything would be square. Using the full face of the wheel as per the video, the disc could push off as you are applying more pressure to the disc. Link to comment Share on other sites More sharing options...
eddie Posted March 5, 2012 Report Share Posted March 5, 2012 The disc in that video, looks supported all the way round, I can't see that pushing off and not being flat? The set up is different, I'll admit to that, quite a clever idea if it works. Or a waste of time if it doesn't! Link to comment Share on other sites More sharing options...
gixerboy1 Posted March 5, 2012 Report Share Posted March 5, 2012 Ever had something on a mag table surface ground and not be flat? Just suppporting the part isnt enough. Link to comment Share on other sites More sharing options...
eddie Posted March 11, 2012 Report Share Posted March 11, 2012 No Only if you have shit under it before you start! Or if you let it get too hot whilst grinding. Unless its bent before you start then thats another matter...................... Link to comment Share on other sites More sharing options...
kaighn80 Posted March 11, 2012 Report Share Posted March 11, 2012 i have a disk facer that i use for cars which has 2 opposing cutters which take off material as the disk rotates, they can be set to do various widths haven't tried a bike disk yet though, does any one have an old disk they don't want so i can try it and see what happens? Link to comment Share on other sites More sharing options...
Adam Posted March 11, 2012 Report Share Posted March 11, 2012 I'd put money on it ending up looking like shit on a floating disk. Link to comment Share on other sites More sharing options...
Mohawk Posted March 16, 2012 Report Share Posted March 16, 2012 You can always try truing the disc by hand. I've done that on a few that had slight warps due to sticky calipers, serviced the calipers at the same time & never had anymore bother with them even under hard breaking but NOT track day use, your mileage may vary ! Removing material does not tru the disc unless you fully face both sides as per the car disc machine mentioned earlier. Bike discs generally don't have enough thickness for this, although your old ones might be 6-8mm thick I guess so may have enough meat. Link to comment Share on other sites More sharing options...
porter_jamie Posted March 16, 2012 Report Share Posted March 16, 2012 No Only if you have shit under it before you start! Or if you let it get too hot whilst grinding. Unless its bent before you start then thats another matter...................... i assume the reason he wants it ground is because it isnt flat in the first place! Link to comment Share on other sites More sharing options...
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