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Member postings for mgj

Here is a list of all the postings mgj has made in our forums. Click on a thread name to jump to the thread.

Thread: Tipped Tools
16/06/2009 18:32:07
Lawrie - that is a very good tip - if you are trying to set your lathe up straight. ie ensure that it does not turn taper. Its in several books - Ian Bradleys Myford Manual, Tubal Cain covers it somewhere, and I think Myfords own instructions cover it too. A Myford has proper screw jacks with which to bring the bed straight.  After doing that check, one can then align the tailstock.
 
Its a standard check that everyone should do when a lathe first arrives, or is moved. And about monthly or so thereafter if accuracy is to be maintained. 
 
BUT with the greatest of respect, it isn't going to sort out finish, unless the lathe is so far twisted that, and it is allowing, or making a clearance for the saddle, and the saddle can then permit chatter. 
 
Of course, all this may just be a matter of the tool being set a touch low, and at the point of cut there is a cross-tip vector which causes tearing.
 
As for measuring and accuracy- I was always taught to take as many roughing cuts as needed. The final margin was always to be divided by 2. so if one had left 20 thou by measurement, you'd take a .010 cut, remeasure and take a final cut. Not too thin so it doesn't rub, but importantly of a size that closely resembled the last measured cut. Thus any spring or whatever in the work would be the same for both measuring and finish cuts and both should cut the same amount. (so what you set as a cut is what you get as a cut!)
 
The only time one should need to take shaving cuts is when deep boring and then the tool springs, so it should come out under power on the reverse cut before measuring, or the hole will come out oversize of course.(as we have all done I guess) Anyway, one won't really get away with shaving cuts in workhardening materials like stainless, should one use that for bits of steam engine, and even some gunmetals. (Same result, different reason)
 
Achievable accuracy. Well George Thomas reckoned that anyone with a lathe in sound condition and decent tools ought to be able to hit a diameter +/- .0002. Within 2 tenths of a thou. 
 

Edited By meyrick griffith-jones on 16/06/2009 18:34:41

Thread: Wheel cutting
15/06/2009 23:47:28
The difference is that on many (most?) lathes the graduations are for diameter - so a movement of say .25" or mm, will result in a change in diameter of .25. The actual tool movement will be .125.
 
On the Myford the graduations refer to cross-slide movement - or a reduction in radius.  So we have to divide by 2 and set the .125 directly.
 
Correct cycloidal profile achieved - unless the addendum has been adjusted to allow a slight clearance and prevent bottoming which would jam both pinions. The dedendum +F,  will certainly be slightly overdeep - and it is the space, not the tooth that is being cut!
In which case you can expect a slightly  "blunt" tipped tooth.  Ivan Laws book Gears and Gear Cutting pp30/31certainly shows that, and the fact that a correctly cut gear engages only on the flanks of the teeth.
 
All these modules and DPs etc have all been carefully worked out, and it would be wisest I suspect to do it to drawing!. The reason for that is that your gears will not maintain constant velocity if the PCDs of the two pinions do not touch. By changing the depth of cut you will alter the PCD of each pinion slightly.
 
One of the advantages of involute gears!
 

Thread: Tipped Tools
14/06/2009 23:34:14
John - I recommend Greenwood too. I think they supply tools with Sandvik tips. Seco tips are very good too. I think the tips supplied by Chronos are mostly Seco, though I don't know about their parting tips. Howver the CCMT -06 tips are. (Greenwoods Kit Q cut parting thing is super - that uses the Sandvik T-MAX Q cut tip N151-250 -5E. There is a 5F tip which I prefer - better finish for a lower feed rate. There are also right and left handed ones to drop the cut off bit, pip free (the designation is N151r/l xxxx etc) thats a 2.5mm seat.
 
Dave, pretty well all tipped tools will seem blunt - - The full designation for the positive rake lozenge shaped tips is a CCMT -06 (cutting length) - 04/08. Nose radius in mm. Most of ours are.4mm radius though the .8 mm are very good for roughing, or producing a good finish. However you do need to bevel  whatever is to fit over it..
 
Your final cut, in crude terms, should not be much less than the nose radius, or as John has said, it will tend to skid - that is the recomendation. However, that normally leads to faulty dimension, and not usually poor finsh. With good tips I regulary take cuts of a thou or so against the recomendation and it works fine - but I am pretty confident that the headstock bearings in both lates are 100%. However, I've never yet been able to skim say 1/4thou with a tip, which I can with ground HSS.  (theSuper 7 has a 3" scale graduated in 1/2 thou)
 
Finish - you can overdrive them. The Sandvik recommendation (for a CCMT 06 for normal finish), is a feed rate of  .1-.4mm per rev. The SECO is rather better. But you'll know because it goes rather graunchy. The chip stops being "nice" and the finish can go. If you are hand feeding you'll feel it instantly. As the tip gets older abrasion affects it, and the finish goes, so does that apply?.
 
i have a suspicion you may have found a slackness in your lathe. Assuming the tool is at centre height, and the top slide gibs are properly adjusted (or the top slide is locked during the cut) and feeds and speeds are correct, and the coolant is good, I'd look at the back of the saddle - the gib there.
 
I had exactly the same problem with a new 6" x37" lathe - actually with both ground and tipped tools. Finish and to a lesser degree dimension went to pot after about 3 months. I think the packing grease, which went hard, and probably wasn't really 100% cleaned off from new under the back of the bed, and within the gib blocks themselves, started to wear out or be squeezed out - anyway, outed one way or another. Another symptom was mild chatter on parting off, until you took a decent deep cut, when the chatter would go. 
 
What was happening was this. Load the tool, and the saddle tilts slightly as the tool bites. As it lifts, the cut reduces fractionally, so the saddle drops, increasing the cut, so the saddle lifts... and so on. All on a small scale of course. Anyway, checked all adjustments, cleaned off the rear gibs with white spirit, and under the rear bed where the gibs bear. Readjusted till I could just detect a drag with a set of spring scales (old fshing ones)and problem gone, and has stayed gone. 
 
As for using tipped tools - well they are only a convenience, if you don't have a proper tool and cutter grinder. You wont take a cut of 250 thou, which is 1/2" on diameter on a Super 7 with a tipped tool in free cutting mild. (CCMT06), which you can with a properly ground up high speed tool. With the late set at 600 rpm it does it on a hand feed without even blinking - reasonably slack belts too! I tend to use them for roughing and cast iron, and grind everything else up on a Quorn.
 
Industry uses them of course because of repeatability, high cutting speeds and because relatively its cheaper to change a tip than to have to get all reground and reset. But for us, I think the convenience comes pretty expensive. 
 
Lastly cutting speeds  - about 600rpm for anything steel or so it seems!!!!
 
3.8 x cutting speed in FPM/job dia in inches. = revs. also applies to milling, but substitute cutter dia for job dia.
 
Cutting speed in mild - I always cut at 100FPM, because Tubal Cain (TD Walshaw) said so somewhere and Tubal Cain was never wrong. And it works well -  tipped or conventional tools.
 

 

 
 

Edited By meyrick griffith-jones on 14/06/2009 23:46:17

Thread: Budget storage
14/06/2009 19:13:34
Are they dangerous? Can be.. Maybe you don't have one?
 
Should you avoid train carriages with one in residence? Well you'd probably not get the chance if it's yours. Somebody else's - well you never know.
 

Edited By meyrick griffith-jones on 14/06/2009 19:16:04

Thread: Slot Milling
13/06/2009 15:57:54
Rike - exciting - well I don't!!!!
 
I like to stand back out of range of the coolant spray and drink my coffee to the accompaniment of that gentle brrrr noise that says a milling job is going OK. under power feed. Improves my wah no end.
 
I don't much like ruined jobs, jammed spindles and busted cutters neither, which is what I find happens if it grabs on the downcut!! Spoils my wah big time - and my wallet.
 
I have a DoreWestbury, which is very carefully adjusted (and very straight too) and a new Warco super major - bit bigger than I expected, since I don't think in Chinese millimetres. Still same cutter in 2 different machines - finish is chalk and cheese.  Rigidity , mass and damping.
 
And no, I don't downcut mill on the Warco either, despite it being large (very) and new (very)  -no backlash eliminators that I know of, and I intend the machine to last, and to stay as straight and as well set up as it is (usual disclaimer). 
 
I'll leave rike exciting to others!

Edited By meyrick griffith-jones on 13/06/2009 15:58:29

13/06/2009 11:26:15
I think a lot depends on the the feed you put on, and the rigidity of your set up compared with the size of the job - and how sharp the cutter is.
 
Personally I think Circlip has offered very sound advice for the man with a small mill, or one who is using a lathe and vertical slide. If one has a big full sized mill, dovetail column and backlash eliminators, then one is operating in a different league. 
 
Climb milling without backlash eliminators? Its the tension on the slide that is doing the trick probably, that and the fact that the chip start fat and gets thin - ie a decent bite for the cutter- so the suggestion might be that the cutter is getting a bit blunt for "ordinary milling". ie its riding up and then biting - or there is some float in the spindle? Or you are not feeding fast enough (too low a tooth load) or the revs are too low? Or you are not locking all the unused axes. Climb milling its seeing the full chip width as the edge engages.
 
Vibration, inherent in milling, is what kills finish, so if one is using a 2 flute slot drill, the 3 flute FC3 type cutters should improve things, because normally you always have one tooth engaged in the job. Being disposable, they are cheap as chips, and double as an endmill too - but tend to be in small sizes.
 
There's no doubt that climb milling is a better option if you have the right kit, - but it can be really really exciting if you don't.
 
With many apologies if I am trying to teach my Granny.
Thread: Material Suppliers
13/06/2009 10:58:01
With respect - no.
 
Firstly if you are not running a business you have no problem. Provided you your activity doesn't constitute a nuisance (noise, hazards like welding flash, paint spray).
 
Second the occasional truck turning up is no worse than if getting bricks, timber or tiles delivered for a bit of serious diy. Its only if things get unreasonable.......

In fact all I do is buy the 3 metre length, and ask the man to guillotine it into 1m lengths  They don't mind chopping it up - its the spare offcuts they can't sell they don't want lying around. They can quillotine up to 1 1/2" dia. On with the gloves and all onto a blanket in the boot of the Fiesta. OK, you lose an inch or so either side of the cut, because of crushing, but if you have 3m of it, 4 inches is not an issue - providing one has ones parting off sorted. Mandraulically hacksawing and facing might be!!
 
The break poimt is about 1 1/4" dia. After that its just easier because of transport and actual usage, to buy a metre for £20 off a supplier - its probably a lifetime buy anyway, or it is for me.

I don't suppose that many model engineers use significant quantities of steel over the 1/14-1 1/2" mark?
 

 
 
 
 

13/06/2009 01:50:59
Yes but...... some of these prices people are advertising you'd be better off buying the full 3 metres of a free cutting mild like 220M03/EN1A , cutting off the couple of foot you want and chucking the rest away!
 
Slightly different with non ferrous.
 
Incidentally there is a big metal wholesalers in Bristol if anyone wanted to do the Yellow Pages thing. They are supplying a lot of retailers in the SW. They only sell in 3m lengths, but that would not be a problem for a club or something to put an order in. They certainly do 220M03 in imperial sizes, as well as the standard engineering grades.
Thread: brazing/siversoldering
11/06/2009 10:37:39
David, as far as I can see, the answer is "It all depends on the pressure and volume of gas that the burner can take compared with the amount delivered by the regulator"
 
For instance, my self blown calor nozzle will blow itself out, because not enough air is getting into it at the back. Thats with a 2 bar regulator. So there is no point it putting it onto the high pressure 4 bar job.
 
On the other hand, the bigger Sievert nozzles, to reach their ful potential, will handle and need the 4 bar. 
 
The likelihood is (depending on the nozzle) is that it will work, but you won't get full throttle out of it. Whether that matters depends on the size of the jobs you want it to do. So much gas  is so much heat capacity, even if the nozzle can handle more.
 
I guess you'll need the bigger regulator in the end - the test will be if you can heat work up without cooking the flux?.
 
 
 

Thread: chain suppliers
10/06/2009 02:13:53
Live Steam Models advertise chain in 3" and 4" scale. They don't give any other details in their catalogue
Thread: British Gunmakers screw threads
07/06/2009 16:44:21
I was told that much of the rifle tooling was transferred to Pakistan - sold to whom I don't know. However you can  get spares for the CF2 series (I needed a magazine floor plate and spring for a .270) and quite possibly the Monarchs. Pakistan was where it came from. So a web search in that direction might turn you up a catalogue or parts listing?
 
Sorry I cannot be more specific.
Thread: Material Suppliers
07/06/2009 00:13:59
Chris - H I live in Kings Stag up near Sturminster. I bought 220M07 free cutting mild from  Pulham Steels. 
 
There is also Dyfed Steels up in Shaftesbury.
 
If you e-mail me we could put an order together - if they want to sell in 3 meter standard lengths.
 
Somdor engineering on the Henstridge Trading Estate have a very healthy scrap bin. A  Mr Ford owns it and is very helpful to model engineers. (Rolled the smokebox for my TE perfectly and for peanuts. Welded up a tuned pipe manifold in ali for a model aircraft ) They don't have much freecutting mild, but could help with more normal engineering grades, especialy in bigger sections/dias/
Thread: Gaskets
07/06/2009 00:03:07
Circlip - thankyou. genius.
 
You have saved me from a fate worse than death. Assembling a 3" Little Samson with all that Foliac graphite stuff.
 
I'll use the .030 gasket material and Foliac to put the cylinder block on, but brown paper and oil seems pretty handy for almost everythng else. 
 
Blue Hylomar is pretty good if used as the packet says, and not just smeared on - but messy.
Thread: Titanium
06/06/2009 23:52:14
I used to get mine as offcuts from aircraft material suppliers. As long as it didn't need to be certified it wasn't expensive in that form.
 
Is this to be used in a steel or other dissimilar metal sleeve or somesuch, and where there is a possibility  of failure being catastrophic?
 
I may be telling my granny, in which case I apologise, but it galls like fury and is very notch sensitive, so tool tip radii are important and the surface finish needs to be spot on. Also it can work harden badly,  rather like stainless, so that last cut for diameter can't be tiddly steell type finsher! Horrible stuff!
 
I have a hangover from my racing days - about 8" long and 1" square. Do you want it? Grade unspecified, but it is most certainly Titanium - grinds with its bright white spark and all.
Thread: Machining cast iron
06/06/2009 23:28:18
Some engineers suppliers will sell single tips. Myford (used to?) sell  sets of inserted tip tools of 10mm sq shanks. They don't use the standard CCMT tips rather the squashed triangle WNMG-06-04 negative rake tips. (Thats the Sandvik number) They come with a .8mm tip radius and are brilliant for cast iron, as well as general turning, so long as the tip radius is not a problem. Produce a near mirror finish, and very economical because you get 6 points per tip, being double sided.
 
They do suffer a bit in iron because of the abrasion, and there is a KR designated tip specially for iron, but they are not so easy to come by, being a bit more specialised, wheras the WNMG tips are amongst the commonest used in industry.
 
The only problem is that most negative rake tools are quite a bit beefier than would fit in most model engineers lathe  - which is why the Myford tools are so handy. You can take much bigger cuts compared with the CCMT 06 tips. 150 thou or so at 600 odd rpm in mild on a Super 7, whereas the standard CCMT tip often gets unhappy at 50 thou. They won't do the 250 thou that a steeply raked ground up knife tool will do in free cutting mild, but even so they will shift some metal without the vast quantities of ribbon like swarf that the ground tool will make.
 
The extra thickness of the WNMG tips also makes them much stronger and less likely to chip in the cast skin during an interrupted cut.
 
So if you can find a set of those Myford tools it would be well worth it.
 
How deep. I'm afraid I don't start at .010 because with a ground up tool you are in the skin all the time. Sometimes that skin is no problem at all, and sometimes its like concrete, and you don't know till you have knocked the edge off your tool in a few seconds! (Especially with some of the cheaper grades of high speed steel which seem to be doing the rounds) I always start with .030 - .050, but as suggested I keep the speed and feed down. One wants to be sure that the casting is securely held of course, (with 3 points of contact if its on the faceplate.
 
A 6" lathe will handle much bigger cuts , but those figures are what I use  on the Super7.
 
 
Thread: brazing/siversoldering
06/06/2009 22:44:38
If you are going the Sievert route (which is probably the best) the trick is to get the right regulator.  They do an adjustable one at 4?bar. Anyway the high pressure one - unfortunatlely not the one in the entry level kit! You can always turn it down when changing the nozzle for a small job, but if you have a lower pressure regulator you can't turn it up if you need more heat, or buy a big nozzle.
 
My Calor kit with their biggest nozzle and medium pressure regulator wont silver solder (with AG2) a 3" traction engine towbar - well not without doing it in several steps, lots of burned out dead flux etc, several pickling stages to get all clean again. General cartwheels and handstands.
 
So I wish I had bought the regulator with a bit more shunt to start with, because they are quite expensive.  
 
 
Thread: Ignition coils for small engines
06/06/2009 13:41:36
I was going to suggest Just Engines. I bought a MVVS 30cc aero engine from them and the ignition system for that is tiny. There is a hall effect sensor in a little pastic mount, so that is a ready to fit unit, a box of electronics about  1.5 x 1 inch as I remeber, and you can run it off a model aircraft nicad pack (4 AA cells or equivalent).. Very reliable. The output is, I can vouch, pretty stunning. 
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