Thank you for the confirmation - I need to work out whether I can make something similar
- Thread starter Mark Davison
- Start date
My current plunger mod (plunger with o-ring) works for a while but eventually fails for the following reasons (at least afaiac):
- internal thread is damaging the o-ring
- small dia of the plunger (6.4mm) limits the size of o-ring I can use
With external thread, I can increase dia of the plunger to (up to 8mm?), which means I can use larger o-ring, plus it doesn't get ripped to shreds when I am inserting the plunger in.
Well worth trying...
- internal thread is damaging the o-ring
- small dia of the plunger (6.4mm) limits the size of o-ring I can use
With external thread, I can increase dia of the plunger to (up to 8mm?), which means I can use larger o-ring, plus it doesn't get ripped to shreds when I am inserting the plunger in.
Well worth trying...
Thanks @bR39Da
They have a whole bunch of 8mm OD to choose from: https://www.123bearing.co.uk/sectio...exterieur=8.0&fld_hauteur=&fld_shore=&family=
They have a whole bunch of 8mm OD to choose from: https://www.123bearing.co.uk/sectio...exterieur=8.0&fld_hauteur=&fld_shore=&family=
Sorry been out of touch for a wee while, so a bit to catch up on on the various comments!
Bit of a bummer that your seal failed - I'd have thought that once you managed to get it in and sealed, you would be fine until the next maintenance cycle, which should hopefully have been years away!
The old lock boss does have a smaller thread into the lock collar than the new ones - it's M12x1 as you pointed out, which does limit an alternative design a bit. The later ones use a U cup type hydraulic seal. I would have preferred to use these, but the smallest I could find was 10mm (probably the size of the new model pistons?). There is no way of getting a piston this size inside an M12 boss (you only have something like 10.7 to play with once you take the thread into account).
The design I'm working on is using an 8.5mm piston, with an O ring seal. This is about as large as I was comfortable going while still leaving some wall thickness. This is a large enough bore that the 8mm threaded actuator can fit inside without touching and damaging the bore. Because the bore is full depth, it can have a tapered entry to seat the O ring, and still leave ample travel (you do lose a bit of travel because of the threaded cap though...). A larger piston would be possible, but the whole piston arrangement would be external to the M12 collar thread.
I'm using M12X1 for the cap as well, and both the boss and cap are having a 16mm hex, so should be easy to get in and out. It will use the standard actuator lever.
Still waiting for my son to machine the boss for me.... He's thinks with the machinery and tooling he has available, we can get the bore finish we need without a reamer (which I don't have, but could get if needed). I gather it's being done in something like 4340.
This is all modelled in fusion - if anyone wants this, let me know your fusion id and I'll share it. But be aware - we haven't built one yet!!
Meanwhile the head is in bits, and all getting ready to repaint in the original (for mine) RAL 7035 grey. I'm using Valspar's Beromix 2000 automotive paint. I've used this previously - it's a 2 pot, so nice and hard, but also designed to not use a clear, so feels ideal for this. Do need to be careful spraying this as with most other 2K paints! Other than the brake, everything else in the head is 100%, which is great since it was dry when I got it.
That's about it for now.
Andrew
Bit of a bummer that your seal failed - I'd have thought that once you managed to get it in and sealed, you would be fine until the next maintenance cycle, which should hopefully have been years away!
The old lock boss does have a smaller thread into the lock collar than the new ones - it's M12x1 as you pointed out, which does limit an alternative design a bit. The later ones use a U cup type hydraulic seal. I would have preferred to use these, but the smallest I could find was 10mm (probably the size of the new model pistons?). There is no way of getting a piston this size inside an M12 boss (you only have something like 10.7 to play with once you take the thread into account).
The design I'm working on is using an 8.5mm piston, with an O ring seal. This is about as large as I was comfortable going while still leaving some wall thickness. This is a large enough bore that the 8mm threaded actuator can fit inside without touching and damaging the bore. Because the bore is full depth, it can have a tapered entry to seat the O ring, and still leave ample travel (you do lose a bit of travel because of the threaded cap though...). A larger piston would be possible, but the whole piston arrangement would be external to the M12 collar thread.
I'm using M12X1 for the cap as well, and both the boss and cap are having a 16mm hex, so should be easy to get in and out. It will use the standard actuator lever.
Still waiting for my son to machine the boss for me.... He's thinks with the machinery and tooling he has available, we can get the bore finish we need without a reamer (which I don't have, but could get if needed). I gather it's being done in something like 4340.
This is all modelled in fusion - if anyone wants this, let me know your fusion id and I'll share it. But be aware - we haven't built one yet!!
Meanwhile the head is in bits, and all getting ready to repaint in the original (for mine) RAL 7035 grey. I'm using Valspar's Beromix 2000 automotive paint. I've used this previously - it's a 2 pot, so nice and hard, but also designed to not use a clear, so feels ideal for this. Do need to be careful spraying this as with most other 2K paints! Other than the brake, everything else in the head is 100%, which is great since it was dry when I got it.
That's about it for now.
Andrew
Funnily enough, I don't think it's a polished surface you want. Talking to an old mate who was in the brake business, and he commented that you typically need to hone brake slave and master cylinders for the hydraulics to work properly. His belief was the cross hatching captured a miniscule amount of oil, and that is what provided the seal.
And just checked the links above, and there is a 8.5 od cup seal available, so that is the direction I'll go. Be interesting to see if I can find them here in the antipodes, but mailing one from the UK is no big deal.
And just checked the links above, and there is a 8.5 od cup seal available, so that is the direction I'll go. Be interesting to see if I can find them here in the antipodes, but mailing one from the UK is no big deal.
perhaps, if I have removed the boss and inserted the plunger from the other end (not past the threads) it might have been OK
but every time I have pushed the plunger in, the thread was shredding the seals
Not quite sure I follow your words
I will send you a message with Fusion 360 id so that can have a look at it, pleaseI am not using Fusion anymore, but still have access to it.
Adrian Nicol
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- Nr Cambridge UK
I just downloaded a pdf for the Hofmann UTH series from https://www.machinemanuals.co.uk/manual.php?p=100 it cost 9.95 GBP but is a pretty good clean scan.
