Machine a head of a bolt

hi, this is my first post and I am very much a beginner to machining so please be gentle with me.

I am about to make a bolt for a swinging arm on a motorbike but I need to make the head as well, is there anything special I should do, I.e. How I set it out and how to machine if?

I have a Harrison L5 with a milling attachment so hopefully I have the tools to do what I need?

Your thoughts would be really helpful

Thanks in advance

Well, as no-one else has (so far) replied, I'll say what I think in the hope that other more knowledgeable people will be induced to reply.

First thought is about the material to be used. If it's anything like the last m/c I had, the swing arm carries a lot of weight and is subject to a lot of wear. On my last m/c I had to have it replaced because of this. So, it seems to me that you will need a strong, hard wearing steel. Sorry, I'm not sufficiently knowledgeable to specify such a steel.

In respect of a presumably hexagon head, you may wish to have a look at p. 110 of Harold Hall's "Metalworkers Data Book" where he gives the necessary formula for producing a hexagon head from a circular rod. The formula he gives is D=1.155 x A where D is the diameter of the rod to start with, and A is the across flats dimension of the required hexagon. No doubt other books will show similar formulae. Note that Hall does state that his constants are rounded up.

If I was doing this, I would turn down the bar to the required shaft dimension leaving a large lump for the hexagon head. You would then have to arrange some sort of indexing arrangement for the milling to create six sides. Can't help you there either. On the other hand, I have a filing attachment for my lathe so would probably file. Still needs a suitable indexing arrangement though. Some people have used the three jaw chuck and placed a suitable bar under a jaw at say the front of the lathe making sure that the jaw is horizontal. Using each jaw in turn, and then repeating with the support at the rear gives six positions. Don't know about accuracy but from personal experience with the general poor fitting of spanners, I suspect it might be ok.

Final comment. On my bike, the reason for the wear was that despite the owner's manual stating that there was a grease nipple, there wasn't. Hence no greasing, and three years later, an expensive MOT failure. Perhaps some thought could be given to fitting one at the same time.

Good luck,

Peter G. Shaw

i always start with a hexagon bar

Do you really need a hex head?

I've had a few bikes were the axle has a cross drilled hole and a flange to stop it pulling through, hold this with a tommy bar. For tightening use socket/spanner on the other end.

Not sure if it will work but here is a picture of a similar axle to what I desribed, this has a simple shoulder.

http://images.motorcycle-superstore.com/productimages/300/0000-Bikers-Choice-Front-Axle.jpg

John

Edited By John Bromley on 29/08/2015 16:12:33

Edited By John Bromley on 29/08/2015 16:14:57

I use EN16T for this kind of bolt, what bike is it for, is it twin or mono shock, the later puts far more force through the swinging arm pivot bolt.

As for the machining the head you could use the jaws on the three jaw chuck as a rudimentary indexer, you could also use the jaw as a method of clamping the lathe spindle in the selected position for machining., or you could put a nut on either end.........

Shaun

just one bolt, I would use a filing rest in the lathe, and a three jaw chuck to index it. That's the way I do singles, it's simple, and probably quicker than setting up the rotary table on the mill.

Ian S C

If you can fit a nut on the thread and tighten it against say, a spacer tube under the bolt head, then you have a simple means of indexing the assembly by gripping the nut in the milling vice. Quickest, easiest and accurate !

An alternative, possibly easier and cheaper, is to use a round bar for the bearing surface, and cut a fine thread on both ends. The nuts could then be made from off-the-shelf nuts of a just-smaller internal diameter, bored out and with a new fine thread (1.5mm pitch?) made by you to fit your bar. These nuts can also be turned narrower at the same settings which would ensure that the thread was exactly at right angles to the (newly turned) face.

This saves money and time making the central bar, and avoids making hexagons.

Hope this helps - Tim

PS I do wish people would give more detail when they ask a Q like this - what bike, how old, why spares are not available, etc. It matters a lot what type of bearing is used for example - rubber bush, plain bronze, needle roller, etc.

Another vote for considering not having a hex head at one end. I've made a few swingarm pivots for various Japanese bikes just as a bar with threads at both ends. I used purchased castle nuts both ends to secure them, with cross drilled holes in the bar ends, both ends, for cotter (split) pins to keep the nuts from ever coming off accidentally. As I recall I used unhardened 0-1 bar for the pivots. Rather than drilling the pivot bar for grease holes, while the swingarms were off the bikes I added grease fittings to them. I did so by drilling a small hole in the bushing tubes and brazing on a 1/4"-28 nut over each hole. Standard 1/4"-28 threaded grease fittings were added later. I made sure there was room for the fittings and that they were not somewhere they could be knocked off by nearby parts or clumsy rider/passenger's feet. Not drilling the swingarm pivot bar in theory kept it as strong as possible in shear where they pass through the bushings. I had seen some pivot bars and axles cracked at grease holes at that point, I was fixing a lot of bikes at the time, so it seemed a good idea to avoid it. Good luck, JD

Guys, thank you so much for your advice, it is really helpful for a beginner.

IC thank you for the advice on the material to use.

To give some background for what the bolt is for, it is for the Kawasaki KX125D1 motocross bike I am fully restoring back to if it had come out of the factory, this is the restoration so far **LINK** the idea is to make two bolts, one for the museum piece one for the bike that I can still ride.

I shall be looking to use a push in oiler on one of the bolts so that I can get Grease to the swinging arm bearings as Peter suggested.

The original bolt has a flanged bolt head which rules out the chance of using a hex bar.

Peter, would you have an idiots guide to your calculation for working out the flanges?

Thanks again for all your help

At the risk of repeating what may already have been said, a few thoughts.

If the pivot is subject to high loads, as it would be on a Moto Cross bike; the material ought to be hardened, (Probably case hardening would suffice. You can buy case hardening compounds for home use. You will need a fairly potent blowtorch. S W M B O will be unlikely to approve use of the oven or gas rings on the cooker for heating to red heat!).

The original bolt was washer faced, so with a Milling attachment, you could start with bar the diameter of the original "washer". You then mill off each side an amount equal to half the difference between the Washer diameter and the Across Flats size of the original hexagon, indexing and repeating until you have a replica hexagon. You will have an end mill in the chuck, so the workpiece will need to be indexed in the milling vice using a protractor, (if not previously marked out) using each cut as the angular datum. The socket or spanner to be used for tightening makes a useful gauge, but don't forget to deburr and very slightly break the corners of the job before checking with the "gauge".

The suggestion to thread both ends, and to use nuts and washers seems to be a good one, if feasible. As is to use castellated nuts and cross drill and split pin, (or use Nyloc nuts on longer threads . Nylon is hygroscopic, so eventually the nylon will likely cause rusting of the threads under it , unless waterproffed with a fingerful or so of grease, afterwards)

For lubrication, I would advocate drilling and tapping one end for a grease nipple, and cross drilling, (at both ends if need be) to meet the axial drilling, so as to take lubricant into the bearing areas. Don't make the drillings too small, 4mm is less likely to clog than 3, but don't go to large and weaken the pivot! The grease oozing out at each end will also waterproof the assembly, as well as reducing wear.

Hope this is some help, if only food for thought

Howard

Just had a look at your restoration page on FaceAche, looks very good, anyhow if you get stuck PM me and Ill machine the bolt head for you on rhe CNC Miller......

Shaun