Due to a communication glitch between me and the house designer my main bedroom is a hundred and quite a lot millimetres longer than I originally had in mind (he took the dimension I said as the room width rather than the post spacing - irritating when it's all supposed to be Segal round numbers). This was noticed early but not considered a big deal. However, I've recently realised that the consequence is that the purlins above it need to be 3640 mm long which is a bit of a pain as the material (C24 150x250) is relatively easily available in 3600 mm lengths but more complicated to get in longer lengths.

Consequently I've been thinking of trimming it down a bit which is more than just a paperwork exercise as the brackets the posts are to sit on are already in place - positioned on threaded rod resined into the concrete pads.

http://edavies.me.uk/2015/03/bolted-to-scotland/

The base plates are 300 mm square with the holes for the rod on 240 mm centres.

Options for shortening are to either remove the existing rods and put in new ones moving the plates (and therefore the posts above) in about 120 mm or to chop off a whole 240 mm by reusing the existing inner set of threaded rods as the new outer ones and putting a new inner set in.

Advantages of the 120 mm move are that the plates finish up better centred on the pads (this end lot are the worst of all and though they technically meet the engineer's spec it's only just and I'm not wonderfully happy) and I have the opportunity to get them spaced just a bit more accurately than the builder managed (and, of course, the risk of doing it worse).

Advantage of the 240 mm move not having to remove the existing rods.

I can cut the rods just fine with my jigsaw or hacksaw but I don't think either would practically cut it flush enough with the concrete so the other option would be to try to screw the bolts out (multiple nuts locked against each other on the thread). Holes could then be filled with post-crete or something to stop water getting in and freezing. Do you think that'd be practical?

Or drill the plate half way, add two more bolts middle of the other sides, probably two would do.

Further any US timber is likely to be the right length.

As Marktime said cutting the bolts flush is very simple with any angle grinder. Then, if I were you, I would drill 4 new holes and resin in in exactly the position you wanted - the old bolts could have a lick of some anti-rust paint if you were feeling really pernickety. This is a sub one hour DIY job (assuming the new holes have been marked out...)

If the design is sound then it should be resilient to subtle changes.

And yes, the design should consequently be able to be tweaked as theory meets practice, and other sayings: http://www.lexician.com/lexblog/2010/11/no-battle-plan-survives-contact-with-the-enemy/

If you drill additional holes, especially in alignment with existing ones, then there's a greater chance of causing or facilitating a fracture in the concrete. And don't forget the expansion of rust over the years, which is powerful enough to lift mountains, let alone split concrete pads.

Lots of good discussion - I'll nibble away.

Posted By: marktimeI think you'd be happier with the 120 mm move so I don't understand why you think you wouldn't be able to cut the existing rods flush, i.e. by grinding flush after cutting.

Just a matter of practicality - I don't have a grinder. Mains ones are cheap enough and I'd no doubt find further odd uses but was really hoping to get the project done with battery tools. (Maybe a mains inverter off my van battery…hmmm…?). Could ask the builder's subby who did the work to come back and do it but really didn't get on with him.

Posted By: crosbieI wouldn't be held hostage by the wood. Get it longer, and if necessary trim it in situ.

Yep, waiting for price from another timber supplier who can do 4.8 m lengths. Still, it took them neigh on a fortnight to just answer an email asking if they could do the timber size at all.

''Still, it took them neigh on a fortnight''

So you went straight to the horse's mouth, then?

Ed,
Makita 18v Li-Ion grinder, with 1.1mm slitting disc will do it, just.
The discs will wear out v quickly, but they are pennies...
I have used Makita Li-Ion 18V kit on sites now for a couple of years now, bullet-proof!

Posted By: Ed Davies

Posted By: crosbieI wouldn't be held hostage by the wood. Get it longer, and if necessary trim it in situ.

Yep, waiting for price from another timber supplier who can do 4.8 m lengths. Still, it took them neigh on a fortnight to just answer an email asking if they could do the timber size at all.

Ed are you getting timber from Caley Timber? They tend to only do full lengths are are normally the best price delivered. Don't bother with emailing them, they are very helpful but a phone only job.

Could you make a separate plate that fits over the existing bolts, but extends in the direction you need and then bolt the bracket to that. May need bedding down on a skim of concrete.

Get yourself a grinder immediately. Amazingly useful tool - you'll wonder how you ever lived without one :-)

And I too can recommend the Makita 14 and 18V kit. (I just bought 2 of their 14V SDS drills to add to the two I already have). Only issue is stupid software in the batteries that will stop them charging on the official charger after a while when there is nothing wrong with them - so you then have to use an RC charger instead.

Strictly you don't have to regalvanise as it still works with small holes in it. But I can see why you'd prefer to cut off.

Ed wouldn't a small 230v petrol generator and mains tools be a good investment in the long run?

Posted By: Ed Daviesbaulked at paying half as much again as the prices on Amazon.

FWIW, one of my carpenters bought a clone of a Makita battery. It appears to be as good as the knock-off Nikon camera battery I bought a few years ago. i.e. make sure you buy genuine branded product

Erm what are you drilling the holes with if you didn't buy an SDS drill? A plain combo/hammer drill? I tested my new, decent (hitachi) combo drill against the 14V SDS Makita. The latter drills holes in concrete _10 times_ faster. The gulf in performace is really quite boggling.

No, the software is in the batteries, but the Makita chargers talk to them over the extra 6-way connector. If you use an RC charger and just connect to + and - then you can ignore whatever handshaking they do (including the "I have been charged 'too many' times" message) and just charge with standard Lithium-ion protocol (CC+CV) which works fine. This could be viewed as over-careful safety features or deliberate 'keep buying consumables' nastiness that printer manufacturers pioneered.

I have a lot of genuine Makita packs which do have good quality cells in them, but you can buy packs with just-as-good cells in for about half the price online. The trick is avoiding the charlatans of course. The cloners are somehow dealing with the on-battery chip.

This comment is not meant to appear rude, but looking at the condition of the concrete bases I wouldn't tighten the nuts up too much on those brackets! Seriously if this was the work of a builder whom you are paying to do a quality job, I would be concerned. I have looked at the webpage you linked to and am surprised the BCO let you get away with some of the misalignment of the brackets on the pads which can be seen in the picture.

I honestly hope it all goes well from here on. Oh and Makita stuff is great, although a grinder will need a lot of batteries to be useful as I am sure you have discovered.