light machining work - DIY or get it done? | GTAMotorcycle.com

light machining work - DIY or get it done?

eng2007

eng2007

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So i bought and incomplete moped project and inherited the reasons why it didnt finish.

Among other things, the folks tried to widen the axle openings in the fork legs to accept an 11mm axle, which is generally an uncommon size but occurs frequently enough in the moped world to warratn the mod. Anyway they hacked up the holes pretty bad and on top of this the widened holes are now offset from the centre portion of where the (very obvious) round part of the fork leg would dictate the opening for the axle would be.

Somehow luck was on my side and I found copper/brass sleeves on ebay from china which are 13mm OD and 11mmID so i think i will go this route. the question is do I try to bore the holes with my mastercraft drill press or take it to my friendly neighbourhood obscenely expensive machine shop?

The forks are NOS suzuki K10 forks from 60s/70s. Theyre simple but hydraulic and of decent quality. Not expensive at all but equally uncommon.
 
putting two holes in alignment if you have a drill press shouldn't be that hard. I'd do it at home.

Caveat; I know nothing of mopeds, I'm guessing there isn't sentimental or real collector value here? If this thing is trul2 valuable maybe let somebody else at it.
 
Machine shop if you want it done correctly the first time, with minimal pain, blood, and/or curse words involved. And if things go wrong, another set of forks.

Honestly...bring them in, chat up the guys in the shop, tell them you're in no rush (presumably you're not?) and that way they can fit the job in during an otherwise slow moment/day - you are likely going to get a better price that way vs presenting them as a rush job that they need to fit into their schedule. Telling them you're on a budget wouldn't hurt, but certainly ask politely for a price beforehand - you may be surprised, some shops will squeeze in little things like this for a lot less money than what people think.
 
I'm all for DIY...but for this I'd want it done with more precision than a drill press. Pics of the fork holes now?
 
I do this sort of thing all the time... there is no way you're going to able to bore a hole accurately enough to friction fit an insert using a drill press.
You'll need a couple of thou interference for your 13mm insert. That means you need a 0.509" hole. Got a 0.509 drill bit? Me neither. I would bore that hole with an adjustable boring head. You could also bore it using a 1/2" then ream it with your adjustable ream.
Your next problem is going to be how to hold or fixture your fork leg. That hole has to be exactly 90 degrees to the travel of the fork leg or you will introduce mis-alignment and "sticktion" when ever you load that connection, and the fork leg is round (which makes it hard to hold), and it is tapered (which makes it hard to hold).

... and if you go to all the trouble of boring and inserting DO NOT insert copper or brass or bronze or anything else soft.
 
here are some pics:









With regards to press fit, im sure some good epoxy would make up the difference if they come out a tad too small or sweating the sleeves in would work if theyre too tight.

Also I dont know if the new holes being a tiny bit out of perpendicular will be a huge deal? This is a moped, not a track bike.

The metal point is a good one though...where the heck am i supposed to find a 18mm long sleeve with an 11mm ID? Im sure getting one made would not be cheap at all.
 
Stop.You are in way over your head with this."Just a moped"...seriously!
 
You're already in trouble.
Those holes are off center, and wallered out pretty good too.
It's do-able... but not by your average do it yourselfer. You'll need some way to index those holes.

... and I'm telling you brass is too soft, and you expect epoxy to hold.
... and yes being perpendicular is vital, even on a moped... if you expect the suspension to work.
How much do you want to pay for this 18mm long, 11mm ID sleeve?
 
This is a machining job of about $250-$300 i think.
 
If you look at the second pic (Right leg) you can see what looks like the original marks from the original holes - I think they were off center to begin with. The extra metal for the fender supports would support this idea (no pun). The mounting area is flat (and should be perpendicular) on both sides so if a jig can be made to grab the leg by this area for clamping to the drill press table, then the hole would be perpendicular too. Yes, Im aware a mastercraft drill press for this kind of work would be insufficient.

A nice steel sleeve, 13OD, 11ID, 18mm long would be worth $20 to me.
 
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@bitzz @ Rob Star, I have next to no machine shop experience, educate me, what would be the process and sequence of events and what machine is required to make this right?
If its a proprietary secret i get it, I'd just like to know more. Thanks in advance.
 
I'm with bitzz. Unless this is for a static display it has to be done right and it's hard to undrill a hole.

Re-drilling a hole is sloppy as the drill tends to flex so it must be bored. The forks have to be securely mounted, not held by vice grips so some time is needed for setup.

Again if the moped isn't going to be ridden there are all kinds of epoxy fixes but if the thing is going to be ride-able sooner or later someone is going to take it to the street with unknown results.

You might want to review the overall project to see if there are more machining challenges awaiting you and your wallet.
 
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As mentioned I can help. We can talk more in PM, but yes I can set those up on a cnc mill and helical bore them in which ever position is needed and size you want.

;) Easy peasy
 
crankcall said:
@bitzz @ Rob Star, I have next to no machine shop experience, educate me, what would be the process and sequence of events and what machine is required to make this right?
If its a proprietary secret i get it, I'd just like to know more. Thanks in advance.
Click to expand...


You can come watch me do it if you want. No secrets. Machining practices are well documented on the interweb ;)

Machines have axis's, that are all deady perpendicular to eachother. You set the part up on a table, and line it up straight in various axis's, then clamp it. You use dial indicators to do this. Then you find a position using other neat tools, or in my case, a probe on a CNC mill, send the machine a little program to cut the hole, with an endmill, and adjust size as need be.

I make stuff like tripple trees and clip ons and other neat doo dads in my spare time for my track bike. I can handle opening up a couple holes for a fellow GTAMer :)



 
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Theres no question that machining would give better results but I don’t think everyone is aware what 70’s Italian mopeds are like from the factory. We are talking stamped steel, pronged fork legs and swingarm ends, plastic swingarm bushings (which insert into tubes welded to the shallow, central frame), and chromed steering head bearings that you can see aren’t round with your eye.

Its because the stock machine rode fine that I’m questioning the application of the perfection of CNC machining to an assembly that functions with much more lax tolerances. Even if the fresh sleeved holes aren’t EXACTLY perfect (using my proposed method above), the nominal size of a bolt is smaller than 11mm (I measured 10.8mm) and the sleeve itself wouldn’t actually be taking all the force – it’s the clamping of the wheel to the legs using the axel that would share the load against the sides of the fork legs.

The points, however, about actually boring the hole exactly where I want it without the drill bit walking around is pretty compelling. I have dial gauges to set out the hole exactly but the inherent flexibility of the rotating assembly in even a decent drill press is a good point.
 
Should drop the "or get it done" from the thread title...
 
eng2007 said:
The points, however, about actually boring the hole exactly where I want it without the drill bit walking around is pretty compelling. I have dial gauges to set out the hole exactly but the inherent flexibility of the rotating assembly in even a decent drill press is a good point.
Click to expand...

If you're feeling ambitious, have the part clamped very well and have a reasonably stiff drill press, you could plunge an end mill to recenter the hole with a drill press. Keep everything as short as possible and go very slow to avoid chatter. Personally I would rather do it in a mill with a boring head, but that's not always an option. I doubt most drill presses could deal with the forces created by a boring head.
 
Thanks Rob Star, that's pretty cool stuff. Having several hundred thousand to spend on CNC , vertical mills and end bores would indeed make the process go better.
I'm always fascinated with this stuff, its one thing to be standing beside a million dollar mill , its another to be able to get it to do what you need and understand the process to get there.
 
I find it pretty amazing too. Heres a video of a NASCAR crankshaft being machined from a solid cylinder.

[video]https://youtu.be/UFNEqY6nn0g[/video]
 
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