|John Coates||16/05/2010 21:25:50|
558 forum posts
I have bought a QCTP from Chronos. It is for a Myford but my plan was to drill out the 7/16ths bore to 1/2" to match the stud on my lathe
I bought some imperial HSS drill bits but my first attempt has not gone well. I put the QCTP in my Chester Champion mill and began at 924 rpm. The drill bit cut a small chamfer at the top of the bore hole but then began to wear a groove in the bit so I stopped. I brushed plenty of cutting fluid on.
Should I use a different speed? I have the choice of 240, 520, 924 or 1640 rpm. I can grind the drill bit on my off hand grinder to remove the groove
Or is my only choice to buy a titanium or cobalt drill bit at prices from £26 to £50 which is nearly what I paid for the QCTP !! (about £60) ?
I have searched this site and found a post about drilling something hardened in a boiler but I felt a separate post bespoke to my problem might help me more
Thanks for any help
|Oliver Lindley||16/05/2010 22:51:12|
|13 forum posts|
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 Coates||16/05/2010 23:00:35|
558 forum posts
Thanks for the suggestions. You've given me two more options
|Ramon Wilson||16/05/2010 23:33:11|
1401 forum posts
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
Edited By Ramon Wilson on 16/05/2010 23:35:43
|Martin W||17/05/2010 00:18:04|
|921 forum posts|
Some time ago I bought a set of carbide, at least that is what I thought they may be, tipped drills that the seller claimed would drill through most things. The demonstration was to drill through files etc which they did. I used them on a variety materials with great success though the tips had a tendency to shatter on an intermittent high torque cuts which of course is a characteristic carbide.
I have seen them or similar at recent shows but can't remember the name of the supplier. Might be worth a trawl around to see if you can locate a supplier of these drills. Another option may be to regrind a 1/2" masonry drill to the appropriate cutting angle and try that. Bolt everything down tightly and use copious amounts of cutting fluid with adequate personal protection.
|493 forum posts|
John, get a 1/2" SDS drill as used in hammer drills and grind the (blunt) point to a sharp form similar to an ordinary drill. A 'green grit' wheel could possibly be good enough for that, better is a cheap Chinese diamond wheel e.g. from ARC Euro trade.
I could drill out a solid hardened collet holder to 16 mm+ dia. to get clearance for holding longer stufff in it.
Btw TiN coated and 'cobalt' drills are not - or at least not much - harder than ordinary HSS.
This is a widely held but wrong belief. The TiN is very hard; true, but it is only a very very thin layer. Touching a hard surface crushes that layer easily.
The 'cobalt' type is afaik only a higher quality of HSS.
1936 forum posts
I was going to suggest the same solution as Ramon. Change or modify your toolpost stud rather than trying what I think will prove to be an impossible task and may damage the toolpost beyond repair. Professional workshops may be able to do something with spark erosion (which is the accepted method of forming hardened materials) but it will probably cost more than a new toolpost for a one off.
If the toolpost is properly hardened no tool will cut it successfully.
|Jeff Dayman||17/05/2010 00:57:25|
|2237 forum posts|
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
1936 forum posts
The English Steel Company (ESC) made very high quality steels and from this, engineering tools such as jobbers drills, milling cutters, taps, reamers and tool bits etc. These were made in normal HSS and cobalt steels. This is what they said in their information manual:
" EASICUT A completely satisfactory quality for general use on all types of turning and boring operations.
EASICUT COBALT (6 % Cobalt). A superior quality recommended for machining tougher materials such as chilled iron, railway tyres and wheels and various types of alloy steels.
Note that they do not mention it's use on hardened steels only toughened materials. Don't wast your money on cobalt or titanium drills for this purpose.
The sds drills Hansrudolf mentions are masonry drills I think, which are basically carbide tipped. Let us know your results as I for one would be interested.
Edited By Terryd on 17/05/2010 01:08:18
|Gordon W||17/05/2010 09:11:02|
|2011 forum posts|
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.
|chris stephens||17/05/2010 12:08:42|
|1049 forum posts|
I am very surprized that the tool post is "hard" hard. I think the problem was that the OP was trying to drill FAR too fast. I would suggest he just sharpened the drill and used minimum speed and perhaps he should try drilling from the other side, just in case he has work hardened the surface on the first attempt.
Going the EDM route is way OTT, I can guarantee that an ordinary carbide boring tool will do the job at home (if used correctly,of course). If he is serious about his machining he should have such a boring tool already, if not now would be the time to get one. Any excuse to buy more tooling, what?
|John Coates||17/05/2010 20:01:38|
558 forum posts
Thanks for the help everyone
I did what Ramon suggested and drew a file across the bore opening on the underside and it scored the metal and chamfered the edge of the hole so it looks like I was going too fast as suggested by Chris
So I can try my original drill bit once I have reground it, or try a SDS bit as suggested by Versaboss or a carbide bit
I have bought a boring head that has two boring tools (RDG boring head) so I can always buy a carbide boring bit for this if the boring tools that come with it don't work. I just need to make a 1/2" draw bar to use it in my Chester Champion
You really are very helpful guys to a newbie like me who is just starting out so a big heartfelt thanks
1936 forum posts
The central hole should be quite accurate to locate on the toolpost stud when finished, you cannot really tolerate any slop, that can lead to movement under extreme conditions which you will experience sooner or later believe me,(although I have only been in the business for perhaps 50 years - what do I know?).
The original toolposts are made to be quite an accurate fit on the stud and I'm not sure that you will obtain the required accuracy unless you can bore the central hole rather than drill it. The drilling process is not that accurate even under optimum conditions let alone the methods you are proposing. The original was probably reamed. An sds drill is only a carbide tipped masonry drill and if you grind it you must ensure that it is quite accurate, remember they are not made to engineering standards.
Best of luck, I hope that your methods work,
Edited By Terryd on 17/05/2010 21:33:29
|Ramon Wilson||17/05/2010 22:37:27|
1401 forum posts
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
|Trevor Drabble||17/05/2010 23:55:54|
288 forum posts
John, Have just read your entry and the subsequent notes with interest. Have you considered whether it would it not be better to produce a new shouldered post threaded to suit the top slide and necked down to suit your new QC tool post ? If, for whatever reason you are unable to do this, how much is a new post from Myford, which you could subsequently turn down to suit ?
1936 forum posts
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.
|chris stephens||18/05/2010 11:43:31|
|1049 forum posts|
Reducing the diameter of the stud might seem the easy option, and indeed it might prove successful. I have reservations about doing. The lathe manufacturers obviously decided that a certain size stud was needed when they designed the lathe, and for those who are worried about sloppy fits reducing accuracy, how does that fit in the scheme of things?
As for sloppy fits on tool posts and the loss of accuracy, in principle the idea has merit but in reality any movement would be taken up by the first "heavy" cut and who of us does not measure before the final sizing cut? Well I certainly do, when chasing tenths or even thous come to that. We are talking here of home workshops where every part is a "one-off" even if we are making a dozen of them. In industrial situations with CNC machinery or even simple turret lathes, rigidity is of vital importance for consistent results as stopping to measure everything costs time and as we all know "time is money".
Lets not get too serious or obsessed, making things is supposed to be FUN!
1936 forum posts
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
Edited By Terryd on 18/05/2010 16:58:39
|Digger DG||18/05/2010 17:46:22|
|3 forum posts|
I dirll 300 series stainless using carbide twist drills without a problem. Assuming your material is SS hardness for a 0.5" drill the numbers are sfm - 166, rpm - 1270, chipload 0.004, and feedrate 10,16 ipm. If using a HSS twist drill (not recommended) the numbers drop to 45 sfm, 344 rpm, 0.003 chipload, and 2 ipm feed. From reading your original post, would indicate that you might have been using too high rpm. Also use a good cutting oil.
I've changed out several QCTP, however never actually drilled new size hole. Either made new stud to fit or made new sleve.
Good luck, Doug
|chris stephens||18/05/2010 18:25:13|
|1049 forum posts|
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.
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