[How-To] Making classic looking motorcycle forks - how to line bore.

tonyfoale

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I wanted some forks for my classic race bike. Cerianis were the go-to forks back in the 60s and 70s so I decided to make my own look-alikes. Here they are fitted to the bike.
Aermacchi 2023 016.jpg

The 60s and 70s Cerianis were made in pieces and glued together, I followed the same method. The main part of these to make is the long aluminium tube to which the oil seal mounting, the mudguard and brake stay and bottom axle pieces are glued. I think Ceriani used epoxy but I used Loctite.
Normal boring in a lathe would have that long tube held in a chuck at one end and open at the other for a boring bar. The length of the tube in this case makes that a less than good idea. Neither the tube nor boring bar would be well supported and chatter and taper would be a likely result.

The way around these problems is to line bore with a boring bar supported at each end.
The first step was to make a holding fixture for the tube. The scrap box yielded up some odd shapes pieces for the job.

Boring Fixture01.jpg

These were milled and bolted together to form a rigid clamp to hold the tube rigidly and concentric with the lathe spindle. The clamp was bored in situ to ensure concentricity. After boring, the Z axis was the only one allowed to move the X axis was locked.

Boring Fixture09.jpg

The next step was to make the long boring bar. I made this from the lead screw of an old lathe. The thread was not ideal to hold the cutting tool so I built it up with a split sleeve. The pictures tell the story.
Boring Fixture14.jpg

Boring Fixture16.jpg

Boring Fixture17.jpg

Then that was drilled and tapped as necessary to hold the tool and allow adjustment.
Boring Fixture18.jpg

Boring Fixture19.jpg

Next we can see the relationship between the work holding fixture and the boring bar. Unfortunately, I cannot find any photos of the tube in the fixture. I can't believe that I did not take such photos but........................?

Boring Fixture21.jpg

Boring Fixture23.jpg

After boring the tubes (I made 4) I used more conventional turning methods to finish the outsides.

OutsideFinished02.jpg

Not shown but the glued areas were knurled to provide reservoirs for the Loctite. A technique that I often use.
Once the tubes were finished the other pieces were made by a combination of milling, drilling and turning, oh and filing/sanding on the axle holders.

DSC_3220.JPGDSC_3221.JPG

Mudguard01.jpg

Mudguard02.jpg



Mudguard05.jpg

TopCaps.jpg

CherryForks-04.jpg

DSC_3219.JPG

Assembled.
ObviouslyItalian.jpg
 
Excellent 'outside the box' thinking on your tooling. What engine is in the picture of the bike?
 
Thought that's what it was and why I asked. In my younger days a friend of mine rode an 'Olympia'. It was an Italian bike of 100cc. Engine looked very similar to the Aermacchi.
 
Amazing work. Wish I could just make things like this at the drop of a hat,lol
 
Ceriani should be jealous. Nice work; nice bike!
 
Beautiful work. May I ask which Loctite you use for those "glued on" parts ?
Thanks
Ted
 
Nice work! Glad you took the time to post the pictures.
 
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