The more and more holes that i drilled in this piece the more and more concerned i became the granite could fracture all of a sudden. I imagine that this is certainly possible if the piece of granite itself had a faultline. Luckily i avoided this catastrophy.

And the gantry rail holes are all drilled finally.

I forgot to mention that after i scored all the hole locations. I coated the face in a protective sticky back plastic sheet. I wanted to protect the polish of the black granite as much as i could.

It is absolutely essential that the holes are cleaned out of all sludge and dust. This is to ensure the optimum conditions for adhesion. With a great deal of care, the granite was turned over and pressurised water used to clean out the holes. A hole cleanout blower was used to remove the majority of the water and anything else that popped out. This was then left upside down for a few days to completely dry out. It didn't need to be that long, but its just how the time fell until i began work on it again. I also used a plumbers blow torch pointed into the hole to loosen or burn off any micro dust. I then proceeded to clean the holes out with a brass tube brush.

I centered all of the inserts onto a rail and inserted the full assembly into the holes.This gave me an idea if any of the inserts were binding on any holes. Everything was ok in that respect, but a few holes required deepening slightly. Sometimes the granite plug does not shear off level, or you simply didn't drill it deep enough.

All of the inserts in this photo have been glued in, but not fully clean up yet.

I have not got a video of the exact process of fixing an insert in. As soon as you mix that resin/mortar you are on the clock to get it done before it sets rock hard. There was no way i was gonna risk making a mess by trying to take a video at the same time. On reflection i could have probably setup a tripod. I will do this when i do thi process again. I still have more holes to drill in the granite.

The holes I were drilling were for M8 inserts. These required a hole of 16mm diameter and a depth of 95mm.

I wil make a video in the future i promise, but the steps are basically as follows....

• Assuming the hole is clean and dust free.
• Prepare your insert with washer and bolt assembly as shown below. Nip up, but do not overtighten.
• For a hole and insert combination like this, i filled the hole using the mixer nozzle approximately 60-70% of the hole volume. Try not to create blocked air pockets inside the hole. If you do its not the end of the world, as you can quickly pull the whole insert out, stick a bit more adhesive in there and try again. At room temperatures you have probably got 2 minutes to get is situate before its too late.
• Steadily rotate the insert into the hole trying to expel the air inside before the cement pours out. If you get stuck with an air lock, the cement if likely to squeeze out very early in the process of rotating the insert inside the hole.
• If neccessary, work quickly, remove the insert and squeeze in again approximately 40% of the hole volume back into the hole and repeat the process.
• The washer assembly acts as a a centering device and it also ensures the insert is sunk slightly below the surface of the granite.
• If you find a reasonably tight fitting washer assembly inside the granite hole, the insert tends not to sink at all.
• You have to make sure you centre the washer assembly with the bolt before dementing in.
• I liked to remove the bolts from the inserts just after the cement had bitten so it was easier to remove any remaining washers that were left. You can also have a quick clean up with a damp rag and or a scraper before the cement truly sets rock hard.
• Avoid getting the cement inside the threads of the insert. I suppose you could always try to re-tap them, but it is a gritty mortar mix if you choose to go with the Fischer Hybrid that i used.
• If you have followed this sucessfully and there are no big voids in your hole you will have no problem whatsoever applying well above the torque suggested by your linear rail supplier.

This is the kind of result you should be striving for. It is clearly not a voidy fill. The insert is sunk below the surface and the thread is not contaminated with cement.