Member postings for James Hall 3

That looks like a very ingenious system Huub - can I ask what the disk is?

Some interesting observations here - for which thanks - in particular I had wondered about the 'fiddlyness' of setting up and the part of the plastic ball. I shall have to ponder, weighing this against other designs that I might come across.

In fairness to Mr Hall I should point out that (while he obviously favours cup wheels - beyond my means) he does NOT advocate grinding on the side of the wheel but its CORNER which, presumably, counts as being on its periphery - my concern here would be not one of safety but rapid consumption of wheels.

I'm a fairly new machinist but have come to the point where I want to grind myself some (10mm) HSS tool bits.

Many years of wood turning have taught me that I'm rotten at any form of freehand sharpening - for those I now have an excellent belt machine.

I have the Harold Hall book on Tool and Cutter Sharpening (Workshop Practice Series 38) which gives a design for a simple sharpening rest to go with my bench grinder.

As a rest it might be simple, but making it would, nevertheless, entail quite an expenditure in time and material so I'm wondering if anyone has made/used this design and how effective it is. As usual help/comments/advice from the 'old hands' would be much appreciated.

Well, thanks once again to all the helpful responses - my apologies for taking so long to reply, but I've been quite badly laid up with the dread Covid.
It's been a case of a little of everything, but pretty much all suggestions have contributed to largely getting rid of my problems: cross-feed gib adjustment, removing a small amount of saddle play, and a slight increase in headstock preload to reduce the small amount of play there.
No idea really on how much to increase preload but warmed machine up first, inserted long bar in chuck and tightened until no appreciable clock movement except due to the quivering of my arm. All the while turning mandrel to ensure not introducing any binding. Then ran machine at full speed for half an hour with no bearing heating beyond a slight warmth - so hopefully got that right!

Slightly worried over gib adjustment which required tightening to an extent that movement is quite stiff before play was eliminated - I can live with that, except slight worry that this might cause accelerated wear on the cross feed drive mechanism.

Dave Halford: You were very close there - tugged hard at top slide and enough movement to produce an audible clunk. Locked saddle and still the same. Cross slide gibs appear to need adjustment as this is where the play is. I'll have a go at them later and report back. Thanks.

Thanks for responses so far:

br: An approach to Arc might certainly be useful - but trying to get a better idea of what is amiss first (i.e. little point in approaching them if it's my technique at fault).

Dave Halford: No problem at all with brass, which leads me to think that it's the greater forces involved in cutting steel which are at play. The problem was last experienced working on an 18mm steel bar projecting around 50mm from the chuck - so I don't think that it's deflection of the work (though correct me if I am wrong). I'll check the saddle.

Recently my (only about 20 month old) Sieg SC4 began to behave oddly - alternating between cutting deeply and not at all over a cycle of many revolutions. This pretty much independent of speed but most obvious on light cuts (which alternated between a good and hopelessly scored cut along the length making a good finish impossible) and parting off where no cut at all alternated with a very deep cut even occasionally digging in). After some 'beginners difficulties' as a total novice with a new lathe I was parting off or producing a good finish quite satisfactorily so this is a problem which has only recently developed. Sharpening HSS tools or replacing carbide tips with new has not helped, nether has speed variation or careful checking of tool height.

I clocked the spindle and found that with moderate (finger) pressure - certainly no more radial force than I would expect to be exerted by a tool - the spindle was deflecting up to 0.02mm from one extreme to the other.

I don't know whether this amount of play is just expectable 'spring' or indicative of the early onset of bearing wear and the cause of my problems - so the opinion of old hands would be welcome.

Howard Lewis: Thanks - I'm beginning to see that my automatic reaction of giving the flywheel a twist when it became reticent to come off the mandrel was probably the last thing that I should have done. I will bear this very much in mind in future along with the need for lubrication.

Ramon Wilson, Nicholas Farr: Thanks for the info. on galling. I found this too, which is informative - https://en.wikipedia.org/wiki/Galling.

Nicholas Farr: Yes, I should have tried drilling it out but impatience got the better of me, I'm afraid.

I'd wondered about a piece of trapped swarf, but 'galled up' is a new one on me - could you educate me here please.

Howard Lewis: Thanks for your response. The flywheel had actually been sitting on the bench while I was turning the mandrel - so if either component was warm from machining it would have been the mandrel and as time passed the fit should have been looser. I did actually try the judicious application of heat to the flywheel hoping that expansion would loosen it - but no such luck.
I successfully machined the replacement much as you suggest.

Peter Greene: Thanks for you response. I see your point, but the flywheel was reamed, so presumably a parallel bore.
This was actually my second mandrel, the first had a slight taper - the wrong way round - so I adjusted accordingly and turned the second pretty much dead-on parallel. The slight taper was imparted with fine emery and much checking with a mic. (about .-0.005 in 50mm).

Thanks to everyone for a mass of helpful and informative replies. I can't respond to every one individually, so I'll try to cover everything in one go.

Though new to model making, I've quite a lot of experience with metalworking and mechanics so obviously tried ploys like some judicious heating of the hub - no good; similarly, the mandrel had a very slight taper and you would have thought that it would loosen up as being slid off it again - far from it. The flywheel went on to the mandrel as a snug fit, but sliding under finger pressure.

I was not surprised that the flywheel casting cracked - I really had to whop it violently to shift the mandrel - obviously taking all precautions against 'riveting in' and supporting the casting properly.

The source of my puzzlement was that things should lock up so absolutely when attempting to slide OFF a slight taper and when it had gone on without being forced at all. As soon as I tried to slide the casting off the mandrel it was reluctant to move, trying to work it by twisting immediately locked it solid.

Lots of advice on turning flywheels here. My choice of using a mandrel is that the bore in the flywheel is the most guaranteed concentric reference for turning the second side. Credit to Stuart Models who were very prompt in sending a replacement flywheel which I managed to successfully machine last night. I used the 4-jaw to centre the inner rim and then machined the first side and drilled/reamed the bore. I turned a fat short mandrel this time, a slightly looser fit (twice bitten) but snug enough to ensure concentricity. The back of the boss rested against the shoulder of the mandrel to keep the casting true at the rim and was pinched firmly against it by a stud tightened into a tapped bore in the mandrel (which was just slightly shorter than the hub). This all worked well resulting in a good finish and wobble-free result.

Thanks again for helping with replies.

Machining my first model from castings, a Stuart H10.

Having successfully machined one side of the flywheel held in the 4-jaw and drilled/reamed, I turned a mandrel on which to mount it for machining the other side - an exact fit required. The flywheel slid nicely onto the mandrel - very nice fit with no play BUT when I tried to slide it off again it was stuck fast. No amount of tugging or twisting would shift it at all. In the end had to drift it out with the almost inevitable result of cracking off part of the flywheel boss.

Can any one enlighten me what happened here and how to avoid it in future. I wondered if it was tiny fragments of swarf left in the bore or on the mandrel digging in and locking it - but the same happened after careful cleaning and trying again in the remaining boss. Help would be much appreciated.

That's a bit of a hoot really when we're talking about an organization that suffered disasters from neglecting to ensure booster o-rings could stand up to low launch pad temperatures and sending off a moon landing mission containing an O2 tank with a history of faults.

"Well, we lost the craft and its crew, but there were no soldering failures".

I have this - printed out and laminated - hanging in my workshop - meets all needs, quick and convenient. Advantage over digital conversions that you can see 'nearest' values at a glance.

https://www.engineeringtoolbox.com/docs/documents/751/inches_to_mm_conversion.pdf

Thanks to everyone for your advice.

I had initially been mainly worried about the contrast on the same surface between smoothed areas as a result of removing flash and the rough sand finish elsewhere. It now seems that more work is really needed to smooth off/fill the rest of the castings if a good-looking model is required.

I'm interested in having models that actually work but would also like their appearance to be as good as possible.

Just removed parts of my first model from castings - a Stuart H10 - from its bubble wrap.

Now I know that it's necessary to file flash and any significant irregularities, and the worst has already been done by Stuart. Where the castings are filed they are, of course, relatively smooth and these areas contrast considerably withe the rough 'sand finish' on the rest of the same surface. I'm assuming that this difference in surface texture will show considerably after painting. Do people, on the whole, worry about this, or smooth by filing/sanding/whatever as much as possible - this would be very difficult on some of the more complex shaped surfaces.

Advice and experience would be much appreciated.

Well, Michael Gilligan, let's hope his grasp of English punctuation was better than yours.

And, gosh, an organizational Web site gushing in praise of its former top administrator - who'd have thought it!

I wonder if engineers actually had anything to do with NASA's successes.

Undoubtedly a great scientific and engineering success (so far, at least). It says a great deal about the current world however that the Hubble telescope was named after one of the world's greatest ever astronomers while this is named after a NASA administrator.