Hornby vacuum pipe magnetic couplings 17mm or 20mm?

[flyingfox4475]

I have tried using the Hornby 20mm magnetic pipe couplings and compaired them to the Hunt ones I have used . The Hornby Pipe couplings seem to measure the same as the Hunt ones. Although the Hunts have to be turned upside down to couple to the Hornby's.

I have yet to try the 17mm ones but think they may be to close and cause buffer lock.

[Aussie Fred]

I got a response from Hornby and it appears I was measuring it wrong. The 20mm does not refer to the couplings actual length. As they said "The 20mm measurement is between the front face of the pockets. So when measuring a pair of couplings joined together, it will be 20mm" - it is just coincidence the 17mm actually measures 17mm in length as well as 17mm between front face of the pockets."

[What About The Bee]

Hi Aussie Fred

Algebra tells me there is an issue somewhere in the numbers.

For the "17mm coupling" Hornby states the 17 mm is between the pocket faces. So the length of two couplings = 2*17mm = 34mm. In order to get 17mm, 8.5 mm of each individual coupling must be in each pocket. Face to face = 34mm - 8.5mm - 8.5mm = 17 mm

So far, so good.

You measure the "20 mm couplings" at 18.88. So two couplings = 2*18.88mm =37.76mm. Using the same 8.5 mm as above, Face to face = 37.76mm -8.5mm - 8.5mm = 20.76mm

20.76 mm is not equal to 20 mm

This means either the "20 mm couplings" measure 18.5 mm by your original method; OR the face to face distance will actually be 20.76mm, not 20mm.

A minor dilemma indeed, made into a mountain by my CDO. That's the same thing as OCD, but all the letters are arranged alphabetically (joke, I do not have OCD).

Bee

[M. Matthews]

Although the Hunts have to be turned upside down to couple to the Hornby's.

 

 

I don’t understand what you mean by this. They’re symmetrical and work either way up as long as they’re both the same way up.

[Aussie Fred]

I will let you know when I get my Hunt's in, but I concur with your logic.

[Aussie Fred]

I finally received the Hunt Magnetic couplings and quickly fitted them to my Bachmann Intercity MK2A coaches and they work well on radius 3 BUT, big fail on radius 2 and the line I want to run them on has two radius 2 curves, so back to original couplings. They should work ok on the coaches I got with my original Flying Scotsman which runs on only radius 3.

[M. Matthews]

What was the failure on Rad 2? Buffer lock? I find this odd as on the mk1’s I have not experienced this and I personally dislike the small gap that the hunts leave on the mk1’s. I did think that the pockets on the mk1’s and mk2’s were mounted at the same height and distance but clearly this isn’t the case.

[Aussie Fred]

What a DUNCE! I forgot that these are english couplings and I put them in upside down. I have corrected it and they now fly around the 2nd radius at 2/3rd power without a hitch. And 2/3 power is the max for those curves anyway. I might try full speed tomorrow, but only to see what happens, but only with no passengers, just in case. Like a good engine driver, I keep to my regulated speeds.

[81F]

Just got my first pair of magnetic couplings with coach R40348 (Mk1 BSO) and am quite impressed and am thinking about testing them on other stock - Any idea which length was supplied with this coach?

Just a quick thought about the two sizes, could the 17mm versions be intended for HO stock and the 20mm for 00 since the proportions are not that far out