How to drill and tap old cast iron balusters from an old cast iron spiral staircase

You may remember from a previous post regarding the spiral staircase we bought at an agricultural auction of all places, we have measured the height from the hall way floor, 82", the treads are 9" in height, we will therefore need nine treads to create our spiral, little tip that will save alot of time, you lay the last tread first, therefore to put the staircase and move it into position is not an option, make a template of one of the treads, copy this how ever many treads you need, this way you can make the staircase on the floor to work out the exact angle of the last tread.

We have cleaned and treated the treads and balusters, now the balusters have the old rust bolts still attached, I have been told to find an engineering company to drill and tap so new threads can to be screwed in to secure the balusters to the treads.

The first company I approached seemed uninterested however they did point me in the right direction, I popped into a hydraulics company that make alot of 24v hydraulic systems.

Dave the owner had a look at the balusters, I told him about the boat, the project what we are trying to do, create a family home on the river that can eventually be moved to various places, the final result being to buy our own plot of land and moor Tino up for good and use the land as a garden, turns out he is a boater and owns a thirty foot cruiser.

He stopped what he was doing and gave me a metal work lesson, he simply sawed of the old bolts ground it down drilled out the rest of the old bolt, tapped the new thread screwed in a new piece, turned it around and done the same for the railing pin, when he finished he got all the bits together put them in a bag, cut down a length of thread, passed them to me and said "Merry Christmas, give me a call if you have any problems",  amazing goes to show there are still alot of good people out there willing to help each other, I walked out with a smile warm in the comfort that when you are doing things for the right reason in life,  good things happen.

Thank you Dave and Merry Christmas to you.