Drill speed and diameter are related to feed and torque. Also having the correct cutting profile, point angle etc. As most of us use generic drills on a hand fed machine with little power we find what works by feel,or number of burnt out drills. Plenty of power calculations from the manufacturers if you want to get technical and have a power feed machine.

Vic:

Thanks for the link to this comprehensive chart.

Some may see the hole saw recommendations as over-conservative.

The B&D pilot/bullet point bits are excellent but look difficult to sharpen; I haven't seen them on sale recently.

For interest, I have used holesaws to cut large holes in the region of 2 inch diameter and more in cast iron. Feed gently from the tailstock at chuck speeds of 60 rpm or less if you can get it and once the teeth are fully engaged in the component, withdraw it frequently to clear chips. If it squeals, a little oil will help, more to lubricate the side of the holesaw rather than the teeth.

On deep drilling in such sizes cut through from both sides to meet in the middle, using the pilot drill as a guide to setting it up in reverse in the chuck. Keep the plug, it could well prove useful another day.

This last point if also helpful in avoiding the snatch on breakthough in any drilling job, meeting somewhere in solid metal is much less traumatic than a grab by the drill flutes.

Regards

Brian

PS Vic I think the speed from the table for the larger drill sizes is to much too high, I suggest half those values; you also need a really solid set up to drill a 1 inch diameter hole with a twist drill; a three cornered hole is often the result as the drill flexes.

A 1” drill would need a sizeable machine. Saw a massive scrap radial machine last week. Must have weighed 4 tons, the column was at least 18” diameter. The speed said 75 rpm for a 3” drill

Big machine, and serious clamping of the work needed! My of fobco bench drill vas a fitted vdf. Magic ! Well worth the money, never had it on the right speed before, and changing speed was such a faff it stayed on one most of the time. Speeds in general look ok to me

Edit. Autocorrect. Fed up with it!

Edited By Zan on 15/12/2018 23:56:28

Not sure if you drive but your drilling practice is akin to always driving your vehicle in one gear, it will sort of go but not to the best of it's ability, costing you both in time, money & frustration.

Tony

It is a useful exercise to make a chart of the maximum size drill bit for each speed of your particular drill and a column for each material you use. Once you have made the chart you will soon remember a lot of the speeds.

Mike