UKC

Re the above using the recommended 16mm drill bit (new not worn) doesn't quite seem big enough, they appear to flare out slightly at the eye end, think I might have read somewhere to just use a 17 ?  or do people just hope they tap in  ? anyone any experience, thanks 

Mr Titt said the following (about 12mm bolts) in another place:

There are three issues, the bolts, the holes and the drilling.

The bolts- we stretch the bolts down to a nominal 11.8mm and to get them straight, the problem is the stainless steel is annealed (softened) to make it easy to work (it is work-hardened when it is made into rods) and this isn´t as accurate as it could be as they drop tons at a time into a cold-water bath. Some pieces are softer than others and so the amount they stretch down and how straight we can get them varies. They are obviously still smaller than 12mm though.

The hole- a 12mm hammer-drill bit isn´t 12mm, it is part of system for masonary fastenings and gives a hole suitable for nominal 12mm fastenings. The fastening should be 11.8mm or less to fit, the drill bit will actually measure over 12mm (normally 12.4mm) but will give a hole smaller than a 12mm round bar will fit into. Because the drill itself is not rigidly fixed (you hold it) the bit normally makes a roughly triangular hole with curved sides which measured across at any point will be 12.4mm BUT a 12mm round object doesn´t fit in, usually around 11.7-11.8mm is the limit (this shape is called a Reuleaux Triangle and is found in things like Wankel rotary engines or as a polygon in British coins and the Canadian loonie Dollar). Four point bits are generally better in this respect as they usually produce a polygon with five sides so the hole is "rounder".
This triangle shape precesses in the hole, that is it slowly twists as you go down making something like a huge thread, it´s actually an advantage normally as it makes the mechanical engagement of the resin better and one reason diamond cored holes never give such good pull-out values no matter how well you roughen the hole later.
The hole not being round AND smaller than the bolt might be gives problems!

Drilling technique- if you push too hard on the drill the triangular effect is increased and worse the drill will tend to wander to one side making the hole less and less straight, with deep holes in the end the drill bit itself will start rubbing and jam, slow and steady is better than forcing the drill bit. To improve the hole one normally runs the drill in and out a few times after the depth is reached, the deeper the hole then more often.
With really long bolts you will have to open the hole out, either with the normal drill bit or go to a larger bit, 13mm bit are available but not as common as 12mm or 14mm, I can buy 13mm in my local store but this isn´t always the case. Using a 14mm drill is no problem for pull-out strength and if 13mm isn´t available then the drill I would use for long bolts.

As mentioned US pattern bolts are slightly different and are made for a 1/2" hole, normally even the longer ones will fit.

They go in no problem except the last bit which is deliberately a drive fit. You can open the end of the hole if you prefer or use a larger drill, just how you prefer. Make sure your hammer is big enough, we use big-wall hammers not those tiny Euro peg hammers.

Thanks for that Jim, makes sense

I use an 18mm or even 20mm bit to open up the hole , and a small vertical channel for with the 16mm bit for the eye of the bolt to sit in nicely

Using 20mm, doesn't that mean that it doesn't tap in at the end, which you might want on vertical or steeper placement?

When they were available, 13mm bits were virtually a perfect size for Jim's twisted rod bolts. However, I've not seen any 13mm bits for sale for a number of years now and I believe most/all UK retailers no longer stock this particular size. 12 and 14mm are freely available though. 

In my experience, Jim's bolts do vary ever so slightly in diameter due to the alignment of the twists, an inevitable consequence of twisting SS rod I expect. So if you carry a good selection of bolts, you'll probably find one that'll fit perfectly in a 12mm drill bit hole, accepting of course that, in reality, the hole will neither be perfectly round, nor 12mm in size.

However, experience has now taught me to preferentially use a 14mm bit (as well as, on occasion, using an even larger bit to initially widen the hole for insetting the eye if needs be). Final placement, once resin has been inserted into the drilled hole (cleaned by both brushing and blowing), is done with a hammer as others have advised.

HTH

Dave 

UK drills on eBay sell 13mm bits. Although not the best quality they are cheap and seem to last ok. I've placed tons of Jim's bolts with them over the years.

Well you wouldn't place loads of these bolts I've got my grubby hands on of Jims with a 13 mm bit, 

This is true, but I think it was fairly obvious I was answering Dave Williams and we were talking about the smaller version of Jim's bolts.

Can't you find 12.5mm bits in the UK? They're perfect for the 12mm glue-ins.

They seem to be available as standard here in Japan.

The UK plan to revert to Imperial measurement so it'll be 1/2" soon anyway.