hard bit when drilling mild steel

[wallace]

I am attempting to make a lantern tool post for my RS lathe. I have some 40mm round bar which I am drilling a row of holes to make the slot for the tool to go in. All has gone well by starting with a small drill and gradually going up in size. I have one hole that will not drill, it has eaten three HSS drill bits. Is it possible to have a piece of steel with a much harder portion buried inside? Any advice would be great
Mark

 

[flh801978]

Depends what the steel is

mild steel should be ok
stainless work hardens like mad
tool steel can work harden easily
what size hole you doing?
can you drill from the other side?
use a cobalt drill?

Ian

 

[wizard]

What make of drills are you using
Are you using a pillar drill?
What speed are you drilling at?

 

[CHJ]

In the past, (post war period) it was not unusual to come across so called mild steel full of hard impurities.

This was due to less than perfect inclusion of scrap, including tool bits etc. in the furnace.

Have you by any chance acquired a sample of this low grade stuff?

The alternate is as mentioned is that it is a higher carbon content "mild steel" and you have managed, due to blunting drill perhaps, to locally work harden the metal.

This summary of specifications may be of interest (My PDF)

 

[wallace]

I am using my wadkin pillar drill which is a fixed speed of 2000rpm, I could do with a vfd. The bits are HSS of various makes some new some ancient. The steel is from a local fabrication place so I don't think old stuff. By the comments so far I think my problem may be hardening of the steel. I tried to make the holes bigger and when it was not cutting I gave up before I ruined all my bigger drills. I did not know the heat would affect the steel so much I was only going up in 2mm increments, I was using oil as well. I think my speed must be too fast and I've created to much heat? Any ideas how I can progress, I need to get to 16mm and I'm at 11mm and then join all the holes together to make a slot with a file.

 

[flh801978]

Blimey
you need to be perhaps at 200 rpm drilling a 16mm hole with lots of coolant.

Start again with a slow speed ( on a different machine)

 

[wallace]

Thanks I thought I was pushing my luck, that's why I was going up gradually. So is the lump of steel I have no use to work with without better quality bits. I think I'll try with a new bit of steel, Whats good as a coolant for drilling

 

[CHJ]

.. So is the lump of steel I have no use to work with without better quality bits. ..

If you have a decent blow torch or a barbecue you could heat the piece of steel to cherry red and cool as slowly as possible (leave in fire) to anneal it.


Trying to work it with drills at that speed and diameter will only result in a similar experience regardless of drill quality.

If starting again, drill a series of small holes around the hole periphery and join them up with needle file/hacksaw blade.

 

[wallace]

Thanks Chas, that makes more sense than trying to drill a 16mm hole through 40mm steel (hammer)

 

[wizard]

The first thing you need to do is sort out the pillar drill, it’s the most useful tool you will ever have then get some dormer drill bits of eBay and learn how to sharpen them

 

[wallace]

That's the type I was using, I'm ok at sharpening freehand as well. Everything was going ok until I got to 9mm mark then it went pear shaped. I think I have a vfd but I'm sure its only upto 1.5hp

 

[wizard]

Drilling at the right speed i use a 3/16 then ½ inch or whatever and will cut through in seconds and a drill motor should not be more than 1 ½ hp

 

[Graham Orm]

What about annealing the steel? Is there any way you can get it cherry red and let it cool slowly that should re-soften any thing that's become work hardened. Then start again with the right speed and a new drill bit as that too will have been heat damaged.

 

[wallace]

I think I'll just get a new chunk of steel, it was only a couple of quid. Wizard the motor on my drill is the usual wadkin beast being 2.5hp and came from the wharfdale speaker manufacturers

 

[AES]

@Wallace:

CHJ has, IMO, posted the best "do it today" solution to your current problem BUT ..... although I have no idea about your Wadkin pillar drill, you really do need to sort out some way of slowing it down if it's going to be any good for "general" metal working long term. 2,000 rpm is high for all but the smallest of drills but that's about as fast that you should ever be running, and as soon as you get above, say quarter inch dia (as a max, ideally an eighth) it'll be much more useful in the, say, 600 or 700 down to 100 or lower rpm ranges.

As you've now found out it's the peripheral speed at the "outside point" of the cutting edge of the drill that really counts and as you go up in size this gets to really very high linear speeds indeed (high for HSS drills and mild steel anyway).

Has that Wadkin really not got any pulleys (I know the name of course but have never seen one of their pillar drills)? How is the drive taken to the quill? Is an electronic controller a possibility?

These comments are intended to help, not criticise.

Krgds
AES

 

[wallace]

This is my little drill, as you can see the quill goes on the end of the motor shaft. Its a lovely drill with a geared table rise and fall and the drill is controlled by a handle or by a foot lever. When I find a vfd it will make this a lot more usefull.

 

[flh801978]

What's the speed on it?
It should be 1440 or 2800 ?

If you put a vfd there will be no usefull power at the slow speeds you need for larger holes in steels

 

[wizard]

That’s not a drill, it’s a very nice router

 

[wizard]

Before anyone says otherwise it’s an overhead router, and I am green with envy. There is no way that will be any use as a drill. There are three things you can do with that. 1 use it as a router 2 sell it on eBay 3 give it to me

https://www.google.co.uk/search?q=w...yMaLB0QWbrIHwDw&ved=0CC0QsAQ&biw=1327&bih=579

 

[Inspector]

Rather than burn though a bunch of drill bits there must be someplace in England that you could buy a tool post like this one either new or used and come out ahead.
http://www.grizzly.com/products/Rocker- ... the/SB1345
Pete