Bath mixer tap query - flexible tails or another option?

[stubertio]

Hi

A semi-productive weekend of DIY. Got the new waste, trap etc fitted to the bath and moved on to the tap once I was happy the waste wasn't leaking...
I removed my almost 30 year old mixer yesterday after much swearing and loss of skin. I have a new thermostatic to fit and I thought it would be fairly straightforward (well of course!).
When I got the old one off I realised that the deck pillars for the new one (grohe 3000) have about 10 of extra thread on them.

I see two ways forward:

1) Cut the threads on the pillars. Only possible problem is that the cut will have to be perfectly square to provide a good mating surface for the fibre washer.

2) Cut the existing feed pipes and replace with either new rigid sections (beyond me) or compression fit flexi tails (think I could handle this).

Which would you do? Any tips on cutting the pillar thread square if I go this route?
Attached are some pics. Access is a real pain so if new copper was to be soldered in it would require a very slim and fit plumber! I'm not sure there's enough clearance but if anyone can give their opinion before I potentially call out a plumber that would be helpful.

Some pics:

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• stubertio
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Any advice from the pros greatly appreciated.

Cheers

 

[TCCHeating]

I wouldn't reccommend trying to cut down the actual tap itself, the easiest way would be to get 2 of these, they are push fit so only one nut to tighten!

http://www.toolstation.com/shop/Plu...r+15mm+x+34+13mm+Bore+300mm/d20/sd2807/p80338

 

[Burnerman]

Don't cut the tap tails.....are the supply pipes 15mm, 22mm or 3/4"?
Maybe its me eyes but I can't tell from here.....
John

 

[neiltheplumber]

Flexi hoses are rubbish. Cut the pipe down and couple back together with full bore isolation valves. There will be more swearing so don't worry, be happy!

 

[stubertio]

Don't cut the tap tails.....are the supply pipes 15mm, 22mm or 3/4"?
Maybe its me eyes but I can't tell from here.....
John

You tell me! They certainly start at 15mm, but the reducer thingymajigs that screw into the standoffs are, I believe, 3/4. Although when I measure them with my callipers they are not 3/4" or 22mm, so I'm not 100%. Based on what I can find on the Grohe website, all of their mixers appear to be 3/4" and reading a bit more about 3/4" BSP leads me to believe that they are actually 3/4" as the 3/4" designation doesn't necessarily mean a measured size of 3/4".
Or am I misunderstanding something?

Thanks for the suggestions.

 

[Galoka]

No, a 3/4" BSP thread doesn't measure 3/4" IIRC The BSP sizes come originally from the internal diameter of the steel pipe for which they were originally developed.

They will be 3/4" BSP. I'd use a couple of flexi's as suggested above - this is just the sort of job they are good for

 

[Burnerman]

OK, the supply pipes are 15mm and they use reducers to come down from 3/4" (popular bath tap thread size) to 15. No problem with that.
You can cut the supply pipes on a straight run and take out a 10mm piece, and then rejoin with compression couplings.
Or, you can use the push on flexy type, but make sure the pipe is polished clean with wire wool or similar. Flexy pipes do reduce the water volume passing through, though.
John