Hi John

 

It sounds like you are trying to drill a material that is harder than your drill bit.

 

If you have a carbide tipped boring tool, it may be worth trying to bore either in the mill or the lathe.  

 

John, What you would like to achieve is going to be difficult.

 

There are drills that will tackle hardened steel but these are normally used to drill ‘from the solid’ the principle being that sufficient localised heat is generated to ‘soften’ the immediate area and allow the drill to cut. You may have seen the ‘Fhrei’ drills demo’ed at exhibitions. Your problem will be that of just taking out the small amount of annular material. Solid Carbide drills will tackle tough materials but the drills are expensive and very easily damaged if not held securely. The slightest deflection will snap them very quickly.

 

The rpms you have available are fairly high for drilling even tough steel (as opposed to hard) for instance a 1/2″ drill in gauge plate in it’s soft state would need to turn at appx 320 rpm (40 ft/Min) and I expect your tool post block to be much tougher than that.

As Oliver suggests you may be able to bore this using a carbide tipped tool in the lathe providing the material is tough as opposed to having been hardened. A quick test for this is to run a fine file lightly across a corner – if it slips and slides across without making a mark then its hard but if you can feel even the slightest resistance to the file its probably just tough steel and should be machinable – just keep the speed and feed well down certainly begin at your bottom revs and work up. If the tool wears you have very little options left. There may be a jobbing workshop in your area with wire erosion capabilities and they could do this with ease though it would probably cost quite a bit but failing that theres what is probably your best option of all – if you can remove it could you not change the stud to 7/16 ?

 

Hope this helps you – Ramon

 

 

No problem at all to do the hole enlargement by EDM John.

 

If you take the block by any mouldmaker or EDM shop (yellow pages or try Google) and you tell them it is for a home shop, and that you are not in a hurry, you may find they will do it for very little money. It is a really simple burn with an EDM 

 

For Google, it’s often as simple as typing in ‘”yourtown” EDM’  or “yourtown mouldmakers” to find a few shops.

 

Changing the stud to 7/16″ is a good option though, as others have said.

 

Good luck, Jeff

Two ideas I’ve tried, both rough engineering. :- Grind masonry drill as  a spade drill, often works, very slow. Maybe the part is case hardened, not thru’ hardened, try a conical grinding bit to remove the corner, then a standard drill.

 

Hi John,

Now you have proved it’s not hardened you should be able to bore this out. It will be a much easier – read controllable – operation to do this on the lathe rather than drill it – set this up either in the four jaw or on the face plate and bore this out at low revs. You will probably have much slower revs on your lathe.  As you can file it it is either toughish steel or possibly a ‘bare spot ‘ on a case hardened surface – I would guess probably the former – but if the latter once you are ‘under the skin’ you should be okay. Either way you should be able to get through at slow speeds with lots of coolant. Your original attempt was way to fast on rpm for both the tool post material and the cutter material. If your resharpened drill will cut at this lower speed then an ordinary HSS boring bar should do like wise just keep it nice and sharp and keep the cuts small – 15 to 20 thou. If it is case hardened then it may dull where it breaks through the skin – assuming you are boring from the base – just check before the next cut and resharpen if neccesary or use a carbide tipped tool if you have one.

 

On the accuracy point I don’t wish to be pedantic Terry but I don’t think the accuracy of the hole is too important. That is …

My QCTP is an original Myford Dickson one and has been in use on the S7since 1979 and on the ML7 before that. It has a through bore of .630 counterbored at the bottom to .780 for about 1/2″ and has a stepped washer on top that locates in the .630 bore. That has a .580 hole in it – all floating around a 7/16 .437 stud! I have often thought that it should have had a ‘proper’ locating spigot and that I should make a thick disc that will fit the stud and that lower register but have never felt the need to do so because of movement during use. Sometimes its sloppiness has actually proved a bonus in being able to move the holder over in one direction or another when it’s been needed to obtain just that extra bit of clearance on something but I agree thats not a good enough reason to have it the way it is . However it certainly has never proved anything other than ‘it doesn’t seem quite right’. On that basis I would think that  a 10 to 20 thou clearance on a 7/16 stud would be fine for this application.

 

I wish you luck in solving your problem John

 

Regards – Ramon

 

 

 

 

 

Hi Ramon,

 

I am reassured by your observations, I suppose I am too swayed by industrial/toolroom practice where the machines are more robust and cuts much heavier.  I’ve never dared to try such ‘sloppiness’ myself  and I’m surprised that it hasn’t shifted even slightly during a heavy cut as the lower diameter is supposed to locate the tool-holder.  Even a slight movement would affect accuracy. Then again as I’ve said before, the empirical can often prove theory wrong. But  again I’m too much of a coward.

 

Before modifying the tool-holder I would still adopt the route advised by several posters such as Trevor.  That is to make or modify a toolpost stud to be able use the tool-holder  itself unmodified.  A stud is easier to modify or make and not such a disastrous loss if it doesn’t go right and you can afford to scrap the part.  Your choice of course.

Hi Chris,

 

I have substantial experience in an engineering design office and can say that most decisions such as the size of the toolpost stud on a lathe would not be made solely on a strength basis.  There would be many other design factors including convention and availability of stock amongst others.  From memory a 7/16 ms stud has a yield stress of around 11 imperial tons and a high tensile one about 4 times that, and of course as you probably know the uts is quite a bit higher still.  So I wouldn’t worry too much in using that size stud. A modified cap head bolt would do a great job.

 

Perhaps I am serious or obsessed but beginners need to be shown that there are often many ways to skin a cat, even in engineering.  As I said elsewhere it’s horses for courses and in this case I know which horse I would choose.

 

And by the way, I enjoy my hobby immensely

Regards

Terry

Hi terry,

Of course you are right about stud size, 1/4″ would probably be enough to do the job but would not look right.  To my mind, doing a dead simple bit of boring or drilling to make a spare  part fit, is preferable to bodging up the lathe to take an inferiorly made or wrong part. Besides, it is much quicker to bore the tool post than to make a stud and then make a(n) handled clamp nut. Make part fit or alter lathe, you choose.

 

Could not agree more about beginners, but should they not be shewn the easiest way first. Surely it is the teachers job to show the trainee the simple  ways of doing things first, then tackle the complicated ones later. What could be simpler than drilling (at the right speed) a hole? If nothing else, the OP has learnt not to drill at full speed, so some good has come from the question.

 

Ask an engineering question and for every half dozen engineers there will be a dozen answers, all of which could be correct.. As an old friend of mine was wont to say ” there are more ways of killing a cat than stuffing cream buns up its a**e!” , a maxim that has guided me for many a year. 

Re your last, glad to hear it but then you wouldn’t do it, if you didn’t would you?

 

Here’s to variety being the spice of life.

 Cheers!

chriStephens 

 

Hi John,

 

Can I ask what make/model of lathe you have. 

 

I am thinking of buying one of these from Chronos and I note that they make the claim of their qctp that all parts are hardened and tempered.  If you can bore it with an hss drill then this cannot be true, so please let me know how you get on.  Indeed if it is hard as they say it will be a problem to bore with Carbide tools.

 

Regards

Terry

 Hi Chris,

 

following my engineering career I taught the subject for 30+ years.  And would quite agree.about the teaching route from basic to advanced.  However drilling or boring a true hole is not really such a simple operation as it first seems, especially if the material is of unknown specification and the Chronos website do claim that their qctps have all parts hardened and ground.  They are misrepresenting them if not

 

As for ‘bodging up’ a lathe,  I can’t imagine what sort of lathe you’re thinking of,  A stud turned with a suitable thread to match an existing one in a cross slide, a simple turned blind nut with a fitted tommy bar, perhaps 3/4 of an hours work?

 

Still I have never minded being proved wrong, as they say, a mind is like a parachute, of most use when open

Best regards

Terry