Turning on two axis
martyn nutland | 09/07/2023 14:02:20 |
141 forum posts 10 photos | Hello All
I'm wondering if you could advise me on this as I'm not sure how to proceed.
Some background. I'm trying to make a front brake adjuster for an Austin Seven with uncoupled brakes (I can't show you a picture because I don't have the part - if I did I wouldn't need to make one!) But for those of you not familiar with pre-1930 A7s the handbrake puts the front brakes on. There's no connection to the pedal which only applies the rear brakes. What happens is the handbrake lever tilts backwards a plate that pivots on the front chassis cross member. The brake rope or cable - there's only one - passes over the plate in two shallow grooves (one on either side of the plate). The rope is tensioned/adjusted/retained by the part I want to make. Basically it's a half moon with a groove round the circumference to seat the cable (5mm diameter). Integral with the back of said half moon is a stud with a lug/button on the end. The idea is a hole in the aforementioned pivoting plate allows the button to pass though then the stud slides up and down in a slot in the plate. There is a threaded boss on the top of the plate with a long bolt passing through it. Tension/adjustment is achieved by screwing down the bolt so it presses down the half moon. Tighten the bolt and you tension the rope, loosen it and you slacken the rope. Simples!
A few dimensions. The full diameter of the circle of which the half moon is a segment is 41.5mm. The half moon is 25mm deep in the centre. The pivoting plate is 2mm thick so the stud needs to be 2mm + x long to extend through
and as the slot is about 8.7mm wide 8.7mm - y to slide up and down. The hole in the plate is 13.75mm diameter thus the lug/button needs to be 13.75 - y
diameter to pass through. None of these dimensions are critical to +/- a mm or so.
At the moment I have 45mm diameter steel stock in a four jaw independent chuck on the lathe and have turned the 41.5 mm x 10 mm section. How do I turn the stud, lug? I'm thinking there's an analogy here with turning a crankshaft. The core of the shaft to take the main bearings must be turned on one axis, but the crankpin(s), off-set by the crank throw(s) need to be turned on a different axis as the workpiece is one and the same? How do you set that up?
I'm very, very sorry this has been so long winded, as I realise the answer for you all will be very succinct. But I did want to place an accurate image of the part in your mind's eye, especially for anyone who doesn't know the part. Sorry.
Best as Always Martyn
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Nick Hughes | 09/07/2023 14:47:53 |
![]() 307 forum posts 150 photos | Part shown here (BK20):- |
Michael Gilligan | 09/07/2023 15:04:03 |
![]() 23121 forum posts 1360 photos | A picture being, so they claim, worth a thousand words [if it’s the right picture] … would I be correct in assuming that Fig. 3 here is the beast in question ? . http://www.da7c.co.uk/technical_torque_articles/braking_efficiency.htm MichaelG. |
duncan webster | 09/07/2023 15:08:45 |
5307 forum posts 83 photos | You either need a long thin tool something like a parting tool, or cheat, bore a 8 mm hole in the middle of the grooved bit and silver solder a stepped boss into it. I know which way I'd go. |
Peter Greene | 09/07/2023 17:05:31 |
865 forum posts 12 photos | Austin 7's have brakes? Holy moly, I never noticed on mine (all those years ago). |
Speedy Builder5 | 09/07/2023 17:22:54 |
2878 forum posts 248 photos | How did the radiator filler cap go ?? Is this what Martyn wants to make (stock item) here?? Several other suppliers stock this, not sure what these are called in France. Bob
Edited By Speedy Builder5 on 09/07/2023 17:23:56 |
Speedy Builder5 | 09/07/2023 17:37:18 |
2878 forum posts 248 photos | Martyn, what year / model ? Bob |
old mart | 09/07/2023 19:43:19 |
4655 forum posts 304 photos | It might be easier to make that part as a complete disc on a lathe and then cut out the part needed. |
Martyn Nutland 1 | 10/07/2023 14:23:20 |
32 forum posts 2 photos | Hello Again All Thank you so much for the responses. Such a diversity I'll respond by name if I may. Nick - exactly. BK20. Michael - that's the adjuster outside the chassis side rail that you use to adjust (as best you can!) the back brakes. Remember, we're discussing the uncoupled version where there's no connexion between front and back! Duncan - Not quite sure how you would use the 'long thin tool' as I think you'd be entering the work on the centre line (axis). So would you be using the four jaw to offset and create a different axis? That said - the cheat is brilliant. I'd thought about it. I guess many people would throw their hands up in horror at the suggestion of silver solder on a brake part. But I think brazing would be absolutely fine. Speedy - That's for coupled brakes and I have a box full. Interestingly, I modified one to use on the pivoting plate of the uncoupled system. It works, but it's too thick to allow the plate (clearance between it and the chassis member) sufficient movement to pull the brakes on. Date and model not relevant here, of course, as pre 1930 A7s had uncoupled brakes (remarkably!) PS Radiator cap worked out fine. It's certainly not perfect, but the very uninitiated probably wouldn't know it's not 'factory (or some factory) and it's better than the 'ole. Old Mart - If it's not too much trouble and you forgive me being daft; could you talk me through? Thanks again everyone. Martyn Sunny/hot in Paris. No riots!
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duncan webster | 10/07/2023 14:49:45 |
5307 forum posts 83 photos | The parts list above suggests that the boss isn't very far off centre if at all, just offset it in the 4 jaw. Can't see any issue with silver solder as long as it's done properly. It is a form of brazing, just slightly lower temperature
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DC31k | 10/07/2023 15:17:49 |
1186 forum posts 11 photos | Posted by duncan webster on 10/07/2023 14:49:45:
Can't see any issue with silver solder as long as it's done properly. If there was any doubt, lightly countersink the main part on the other side to the button and peen over the shaft. If there was a failure of the solder joint, the shaft will just rotate and cannot come out. |
Martyn Nutland 1 | 10/07/2023 15:18:37 |
32 forum posts 2 photos | Duncan That's basically what I needed to know and as you have observed the offset doesn't to be very much. I probably made a mistake in that I didn't use the large ( all things are relative ) four jaw independent I have. But I still have enough to move the axis. Point taken about silver solder. That's why you should use it for petrol pipes so it doesn't melt in a fire! As you say fine in this context. Thanks again. Martyn |
Michael Gilligan | 10/07/2023 17:49:59 |
![]() 23121 forum posts 1360 photos | Posted by Martyn Nutland 1 on 10/07/2023 14:23:20:
Michael - that's the adjuster outside the chassis side rail that you use to adjust (as best you can!) the back brakes. Remember, we're discussing the uncoupled version where there's no connexion between front and back!
That’s strange … I had deliberately chosen Part.1 of the set, because I thought it specifically mentioned the earlier version. Ho-Hum … must try to get more sleep. MichaelG. |
Harry Wilkes | 10/07/2023 18:09:26 |
![]() 1613 forum posts 72 photos | Posted by Peter Greene 🇨🇦 on 09/07/2023 17:05:31:
Austin 7's have brakes? Holy moly, I never noticed on mine (all those years ago). Me too stopped mine like Fred Flinfstone H |
Howard Lewis | 11/07/2023 22:29:48 |
7227 forum posts 21 photos | My only suggestion for making BK20m would be to turn a complete didc, and to produce the groove for the cable using a round toolbit of the correct diameter, ground to act as a cutting tool. Having produced a "pulley" like component, then cut out a scetor of a suitable size and then make and fit the headed pin to it. Howard |
martyn nutland | 12/07/2023 10:06:33 |
141 forum posts 10 photos | Got it, Howard. Thanks. The consensus seems to be, then, make it in two parts and forget machining as one piece. Fair enough. Martyn
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Stuart Smith 5 | 12/07/2023 11:02:28 |
349 forum posts 61 photos | Martyn You could make it as one part. Turn the outer diameter and then the groove for the cable either using a custom tool or a profiling tool. Then offset the part in the 4 jaw and turn to the outside diameter of the lug. Then turn the smaller diameter of the lug using a parting tool or a custom made tool.. Reset the part in the 4 jaw and part off (the large diameter). Then cut off the unwanted part to make the crescent and file to shape or if you have a mill, use that. I am no expert, but that is what I would do. Stuart |
martyn nutland | 12/07/2023 11:24:08 |
141 forum posts 10 photos | Thank you, Stuart. This was my original thought - more or less. I now have two options. Making it in two parts is definitely simpler, but is not as it was done originally. But then, that doesn't really matter because it was probably a stamping job and certainly not machined. My nervousness about trying to make it as one piece centres on off-setting when there's such a disparity between the diameter of what will be the segment (41.5mm) and the button (about 13mm). As I said to Duncan, I've probably made an initial mistake in not using my larger four jaw that would have given me more latitude (sic). I'll let folks know how I get on. Meantime, many thanks all. Martyn |
lee webster | 12/07/2023 12:35:45 |
383 forum posts 71 photos | If you can't buy the bits you need from one of the A7 parts suppliers, why not wait until the Beaulieu autojumble? I know it's probably a few months away, but I bet you get get a list of other bits you need to make it worthwhile. It's also been a few years since I last went to the A7 national show at Beaulieu, But again, well worth a visit. I don't know when that show is on either. Are you in Paris? A long way to Beaulieu, but I have seen many French paople and cars when I used to go. |
Martin Johnson 1 | 12/07/2023 12:59:40 |
320 forum posts 1 photos | If I am making a part like that (BK20), I would start by marking out the two centres (pulley and boss) on the stock. Put in small centre drill pips on both centres, then it is very easy to centre on each axis using the 4 jaw chuck. If you wanted to go there, you shouldn't have started from here. Martin |
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