How to cut these slots?

[Ian ParkinParticipant @ianparkin39383]

I’m making a new flat top yoke for a motorcycle to mount handlebars onto directly..

I’ve cut out a blank and bored the holes on the lathe and it fits well on the forks

however i have to cut the clamping bolts slots…

the back one is easy on the bandsaw but any ideas on how to cut the internal ones

the holes are 35mm diameter and the alloy is 25mm thick…

[JasonBModerator @jasonb]

If you are happy with a bandsawn one for the easy cut then a hacksaw should do the others

[Clive FosterParticipant @clivefoster55965]

Hacksaw works OK but you may find the slot bit narrow.

A power hacksaw blade is wider but harder to control. A relatively fine tooth one works well enough to enlarge an ordinary hacksaw blade slot.

Stiff enough that you don’t need a frame, wrapping a few layers of duct tape around the end of a broken one to form a safe handgrip makes a useful tool for this sort of thing.

Clive

[Ian ParkinParticipant @ianparkin39383]

Actually i thought a jig saw with a Coarse wood blade should do it but I’ll bear in mind the power hacksaw blade Clive

[DC31kParticipant @dc31k]

Two hacksaw blades in the same frame to achieve a wider kerf.

As the item is flat, you can clamp something hardish top and bottom (4 pieces total) to act as a guide so the cut does not wander (test cut on a piece of scrap so you can measure the kerf and thus the spacing between the guides.

If you are jigsawing, you can clamp a similar guide on to ensure a straight cut.

Are the yokes to be further reduced in size to more closely resemble the original? If not, the two slots you want to cut may not clamp up as there is a lot more metal surrounding them.

[Ian ParkinParticipant @ianparkin39383]

DC31K. Sure they will be as original size wise the originals are cast and the underneath is hollow perhaps only 10mm thick in the middle section..not sure how to deal with the lack of squeeze..

[Grizzly bearParticipant @grizzlybear]

Squeeze.  Drill, tap & grub screws in addition to your squeeze.

Good luck……..

[Clive FosterParticipant @clivefoster55965]

Two hacksaw blades in one frame is common tip for wider slot. But I could never get a pair to work properly to cut a neat slot.

Put it down to the blade tensions being a bit different. The mounting pins on all my frames have significant angle pointing out of the ends of the frame to ensure the blade doesn’t ping off when tightening. So the inner blade carries less tension.

When the Rapidor power hacksaw broke a blade I said “Ah ha” and made half into a knife and half into a slot widener. The knife is great, takes a really keen edge. The slot cutting thingy gets used about once in 3 years!

Clive

[VicParticipant @vic]

I like things neat and tidy so I’d be tempted to try milling a slot with a 1/16 slot drill on some scrap material first? None of mine are long enough so it would need to be cut from both sides.

[NimbleParticipant @nimble]

Hi Ian,

My suggestion would be to  invert a jigsaw and mount on a wooden platform. Use a metal cutting blade and cut the necessary slots using a guide to keep slot in correct place.

NimbleNeil.

[Phil PParticipant @philp]

I think you will find that the slots will not give enough grip to the fork stanchions even when done up very tight.
The material will be just too stiff to deform enough.

Why not use some split cotters a bit like this idea.
https://toolingaround.ca/lmb4.php

Phil

[Ian ParkinParticipant @ianparkin39383]

Phil the split collets are a great idea but I’m slightly worried about locally crushing the stanchions..they are quite thin wall and with  an internal thread for the top nuts to hold onto to

[Phil PParticipant @philp]

I wonder if you could put a slot right across between the two stanchions, that way you should be able to get in with a slitting saw, the long slot should weaken the material enough to get a grip with any luck.
You could actually remove some of the material between the stanchions at the front of the slot so you are left with shorter slots at either side with a couple of clamp scews on each. As per fag packet sketch below.

[duncan webster 1Participant @duncanwebster1]

If you go to rsonline and search for locking bush you will find clever taper affairs that might obviate the need for slots. You’d need to bore the holes bigger, looks like there is some scope as wall thickness appears greater than original

[bernard towersParticipant @bernardtowers37738]

The slots on my bikes are quite large one is 5/32 so why not mill with a long series cutter

[bernard towersParticipant @bernardtowers37738]

Correct me if I am wrong but those slots dont look symmetrical, the one at the top looks to be the one that is right as its angle has thinned the material to be pinched by the bolt. Just an observation.

[Ian ParkinParticipant @ianparkin39383]

Duncan I haven’t seen those locking bushes before on any machine I’ve come across and they surely would work but the outside dia on this fenner one is 60mm so it would need to be lots bigger round the stauntions..

this more pics of the original dropped yoke and my new one awaiting final finishing but the hole with the cut to the outside which I’d imagined would clamp up nicely doesn’t at all…

[Clive FosterParticipant @clivefoster55965]

I imagine that the considerable reduction in thickness over the central potion of the original, cast or forged, yoke compared to the outer web and the immediate surroundings of the holes influences the ability of the slot to close up when clamped.

My one and only experience of making special triple clamps (yokes) was well over a decade ago but, as I recall things, the first test with the material still of constant thickness was very unwilling to clamp up. I think it sort of did but the bolt torque needed seemed dangerously high. For reasons I can no longer recall it had to be thinned down in a manner very similar to a standard cast yoke. After thinning the clamp bolt torques dropped to more reasonable levels.

Factory pinch bolt torques are quite low. For example the manual for the rotary engined Norton Interpol 2 that I have immediately to hand recommends 22 to 24 ft lb on the tube pinch bolts and 18 ft lb on the stem pinch bolt. Which seems fairly typical for modern alloy yokes. So clearly things are inherently fairly flexible.

Back in the day, before (apparently) all the world and his wife had a CNC mill in the garage and the billet craze undreamed of, many aftermarket top yokes seemed to be basically a quite thin plate with slotted tubular extension affixed below to actually grip the fork tubes and stem. Which always seemed a bit scanty to me. But BMW used what appeared to be a chromed off-cut of 3 mm (or thereabouts) sheet steel as their top yoke on the R series airhead twins so presumably the engineering worked out.

Clive

[Ian ParkinParticipant @ianparkin39383]

Clive

i have a r100 with the thin steel top yoke the nuts hold the tubes in place…an iron head Harley has 35mm tubes but they have tapers on the end of the tubes that fit into the top yoke..alloy with matching tapers and held on with the nuts.

these are for Ceriani type forks I don’t seem to be able to find a top yoke with handlebar clamps or so i can drill for risers..

i suppose i could make new longer nuts and fit the tubes into a new top yoke say 20mm into 25mm thick material then use the nuts to hold the tubes in place in place?

The only problem with is this theres only 1.2 mm for the shoulder

[Ian ParkinParticipant @ianparkin39383]

Another thought i could make a collar to fit under the top yoke say 20mm thick to clamp onto the tubes to stop the tubes pushing through the top yoke? Maybe 60mm dia with the hole slightly off centre to allow more room for the clamping bolt

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