Member postings for Robin Graham

Thanks for replies, and apologies for not getting back to this sooner - my wife has taken on a foster dog so I've been in woodworking mode making stair gates. C'est la vie!

William - many thanks for the info about Whitaker rings. I'm not convinced that's what going on here though - brass, very light cuts (~10 thou) slow feed. But maybe - and valuable info even if it isn't.

Bob Stevenson - I was initially sceptical about 'stages of resonance', but changing the spindle speed from 550 to 700 rpm gave different 'zones':

and returning to 550 gave results broadly similar to my first photo:

So it's mechanical. I think I understand what's going on now.

On the optical effects, I found, unsurprisingly in retrospect, that the 'spectrum' was very much dependent on camera and lighting angles. Thanks Martin.

I doubt that I can get much further in understanding optical effects without specialist kit - a trichroic beam splitter would be an absolute minimum requirement I expect. Sadly , I haven't got one.

I should just be happy that I can get this finish on a mass-market hobby lathe.

Robin.

Edited By Robin Graham on 30/07/2021 01:21:13

Edited By Robin Graham on 30/07/2021 01:28:35

My take on this is based on experience with Sorby Pro-Edge, but may be useful.

Does anyone think this is a viable method for maintaining tools (and drills with a drill jig).

Yes, I frequently use the Sorby for this sort of thing. I can't see why the cheaper Clarke linked to wouldn't work, for HSS at least, given suitable belts.A caveat is that the Clarke runs quite a bit faster than the Sorby - 13.5 against 3.7 metres per second. I don't think that would be a problem for HSS (bench grinders run at an even higher surface speed), but it would be too fast to be comfortable for carbon steel.

Do the belts wear out too quickly to be useful?. I know how quickly wet n dry paper loses its edge unless used with soap n water.

No, they last surprisingly well.

My own experience with wet 'n' dry is that if used dry it clogs well before it lose its edge. My take is that using lubricant is more to do with mitigating the clogging problem than preserving the edge, but I may be wrong. Belts also clog before they become blunt, but can be restored to near pristine condition with a latex cleaning block such as this .

i think i ve found some answer, you need 760mm belts of zirconia or ceramic (ca £5 ea)

Personally, I've found alumina belts OK for most things - they don't last as long as zirconia, but are very cheap. I've never tried ceramic, so can't comment, but if you want fancy, 3M trizact are the dog's and last for ages - they seem to be available in most sizes.

Robin

This is a bit of an academic question really, but I am intrigued.

Facing off a 2" brass bar this evening I noticed this pattern:

It's not a great photo (best I can do with my 'phone) but you will perhaps be able to see five distinct 'zones' going in from the circumference to the centre. The boundaries are very well defined - it's not at all like the effect one sees with tool chatter or that sort of thing.

I did wonder if it might be purely an optical effect - at certain angles there are diffraction patterns:

which seem to coincide, roughly at least, with the 'zones'

I'd be interested to hear any opinions.

The question is academic because the part will eventually be polished, but I'd like to know what's going on.

Robin.

Interesting - thanks for the link to the Smithsonian article Michael. Of course Punch saw what was coming as early as 1906:

I'm a bit confused by the 'mobile' pedantry - every dictionary I've looked at gives "able to move or be transported easily from one place to another" as the first definition. That fits the bill surely? No need for a motor or wheels. But usages and meanings shift - they are mobile perhaps!

Robin.

Edited By Robin Graham on 22/07/2021 23:44:51

Thanks John. I too wondered about 'nominal 14W RMS' - I think I know what RMS means but 'nominal'? I've never understood what 'Peak Music Power' means either. In the course of the weed-out I found some Panansonic speakers which which are rated 30W (Music) 15W (DIN). Presumably DIN is another standard. The great thing about standards is that there are so many of them, as some wit wisely said.

The input for these speakers is 12V AC, so smoothing the input is obviously not an option.

On further thought the work/expense to get them going just isn't worth it. I really hate junking stuff that could be repaired, but it seems that's the way of the world at the moment.

I'm going to have to steel myself for more of this - I'm lucky to have about 550 square feet of potential cellar workshop space, but at least half of it is full of rubbish.

Does anyone want a 10kg box of assorted wood screws ,or a 32 inch flat screen analogue TV weighing 17kg? Probably not.

Robin.

Thanks - despite assiduous searching I hadn't found that. I'll take the risk with the 2.5A adapter then - if I use the speakers myself it'll only be to for TV, I won't be pushing them.

Robin

I'm having a weed out and a pair of Creative T20 mf1545 active PC speakers has turned up. I was going to junk them, assuming they were rubbish, but a quick internet search suggested that they're actually quite good of their kind and worth passing on even if I don't use them myself.

I can't find the power supply though. The power input is marked 12V AC, but no current rating.

As far as I can discover the speakers are 14W 'nominal RMS' each. The beefiest cheap 240V to 12V~ PSU I've found so far is rated at 2.5A, 30VA. Do you reckon that would do? If not, any other suggestions?

Robin.

Thanks for further replies.

soi keo blogfb88 - thank you for taking the time to respond, and welcome to the forum. If you re-read my opening post you will see that I had already considered the possibility that I was cutting a screw thread before I posted, and rejected the hypothesis for reasons given in that post.

To wind this up (for me, for the present at least) I dug out the 4-way TP which came with the machine. When I bought the lathe (new) from Axminster it came with the QC mounted, and I just went along and used it without much thought.

I put the 4-way in place:

shimmed up a tool (PITA) and tried a cut under the same conditions as in my OP:

OK, not wonderful, but no 'screw thread' or other weird patterns at different spindle speeds.

Eventually, after further experiments using the 4-way the part I was trying to make came out like this, straight off the lathe:

Well, OK, I polished the winding handle, but the rest is as-turned. I'm pretty happy with that. Well, f*****g delighted actually.

Many thanks, and especially to Graham Meek who pointed me in a direction which wasn't on my compass, but seems to be the way to go..

Robin.

Edited By Robin Graham on 04/07/2021 23:10:21

Tony - thanks,that clarifies your earlier comment.

Gray - thanks for your detailed reply. I was finding it very difficult to understand why the effect was more pronounced at larger diameters, but maybe you have explained it. Here is a photo of my QC tool post in a typical configuration:

Thanks also for you general comments. I have found that CCGT inserts (the ones I have are from ARC) are OK for finishing cuts in steel - this is an 8mm shoulder screw in silver steel I made tonight:

which was finished with a ~ 0.05mm cut. I'm happy with that sort of finish.

I was interested in your comments about gear head machines as well - I had wondered if there was any point in converting the machine to 3-phase when there are other, perhaps more important, sources of 'noise' in the power train.

Robin.

Thanks for further replies.

John (DMB) - I think I once made a tool similar to the one you describe (it made a shear cut and produced that feathery swarf), but I'd forgotten about it - happens all too often these days. Thanks for your suggestion.

Diogenes - the OK finish on the already reduced diameter was largely due to Hermes, the God of wet 'n' dry. My lathe's gearbox doesn't allow the leadscrew and the power feed to be engaged simultaneously, so that's not the problem, but thank you for your input.

Tony:

"You are also only just 'skimming' the cold rolled bar stock. I have seen this effect on 3 phase lathes as well so not sure it's the motor?"

Can you elaborate on that? Is that something to do do with a 'skin' on cold rolled stock? I'm not sure if it's germane to my problem - I saw the effect with deeper cuts, but posted the pic of a skim the hope of ruling out issues of lathe rigidity.

Chris - twin smooth V belts. I have no idea how well the belts are matched though. I suppose if they're not well matched, it could be a cause of vibration. Thanks for pointing up that potential problem.

John - the surface finish formula is interesting, but also (for me) frustrating - the author doesn't explain how he has arrived at it. There are are only three quantities in the formula - Ra number, feed rate and tip radius.. Presumably that means that other factors such as depth of cut and machine rigidity are negligible in his environment. Not so in mine! Maybe it's a CNC thing. I've no experience myself, but have seen the machines working and they seem to go for repetitive fast shallow cuts rather than hogging the metal off.

Regards, Robin.

Thanks for replies.

I didn't give numbers for all the speeds/feeds I tried because I didn't document all my experiments - that would have taken me a very long time!

The photo I took was 'posed' just to give an idea of the sort of thing I'm seeing - it was a light skim (perhaps 2 thou) on a 3.5" EN1A bar using a fresh 0.4mm tip radius CCGT insert. Turning speed was 550rpm, feed about 0.05mm per rev - obviously not the sort of thing you'd normally do, but I was trying to understand what was going on, and searching (unsuccessfully) for some sort of pattern to the patterns I was seeing. Reducing the spindle speed to 65rpm (the lowest I can go) , but leaving everything else the same, the cross-hatch pattern appears.

In my opening post I mentioned that it's a single-phase machine because I wondered if that might be relevant. After reading Martin's reply I listened diligently to the machine and felt its various parts while it was spinning under no load. There is a definite hum and I can feel 50Hz-ish vibration just by putting my hand on the tailstock. I'd not noticed the hum before because being a gear-head machine it's quite noisy, and I wasn't listening for it. It's most noticeable at low spindle speeds - something to do with resonant frequencies I suspect.

If this is the cause I guess I have to live with it or stump up for a 3-phase motor/inverter.

Robin.

Edited By Robin Graham on 29/06/2021 01:52:04

I'm at my wit's end trying to diagnose the underlying cause of this problem. I was turning some 3.5 inch EN1A today and was unable to get a decent finish, despite trying a number of tools, speeds and feeds. An example:

On the larger diameter part of the work you can perhaps see something resembling a fine screw thread. An immediate reaction would be that the feed is wrong for the tool tip radius, and it is indeed a fine screw thread. But it's more complicated than that - the 'pitch' of the pattern has no simple relationship to turning speed and feed. In fact certain speed/feed combinations give a sort of cross-hatched pattern, like right and left hand threads intersecting.

I've spent an afternoon experimenting with various tools - both carbide and HSS, and different speed and feeds, but always see some variation on this theme. Can anyone shed light?

Ancillary info:

- The lathe is a single-phase 1.5kW gearhead - fairly rigid, about 600kg.

- I don't notice the effect on work below ~2.5 inches in diameter.

- The same thing happens with or without tailstock support.

Robin

Edited By Robin Graham on 26/06/2021 23:48:07

Edited By Robin Graham on 27/06/2021 00:26:26

Me too Dave, on all counts. Your 'bleeding obvious' BODMAS mistake is interesting. Back in the day I would have students come to me shamefaced because they'd spent hours (days even!) trying to debug their code, and couldn't figure out where they'd gone wrong. Blame the computer! Invariably it was a simple BODMAS type error, which I spotted quickly because I was reading the code with an unprejudiced eye - in trying to debug my own code my eye would just run uncritically  over a similarly simple error, following the original track of my mind.

Back to machining - I decided to make the boss for the handwheel separately planning to to braze or glue it into a disc which would be the handwheel. My latest schoolboy error - I turned the boss, drilled and reamed 12mm to fit the machine spindle, then bored 19mm H7ish (that's a new ISO standard) to fit the gear:

I then realised that I had no easy way of enlarging the 10mm gear bore to make a smooth transition to the 12mm bore in the boss. The gear will be fixed in the boss by a grubscrew - I should have fixed them together before reaming. Doh! I think I can get away with it, but I'm annoyed with myself for not having thought it through properly.

To give context, the project is a replacement wheel to fit this arrangement:

The spring pushes the handwheel toward the operator, which allows a dog-point grub screw in the handwheel boss to engage with the spindle and actuate the blade rise/fall mechanism. Pushing the handwheel in disengages the dog and engages the plastic spur with the steel rack to give blade tilt. With, you'd think, perhaps,

an inevitable result.

2,5 hours and counting....

Robin.

Edited By Robin Graham on 24/06/2021 23:58:23

Edited By Robin Graham on 25/06/2021 00:07:10

Edited By Robin Graham on 25/06/2021 00:11:36

Edited By Robin Graham on 25/06/2021 00:17:16

Thanks for replies.

Mostly I just potter about in my workshop for my own satisfaction, but sometimes I'm approached by people who want one-off things made, and sometimes I actively offer to do stuff just because it seems crazy not to. An example from the latter category would be a set of collets for a Multico morticing machine - commercially available, but at insane prices. I've had a lot of help from from the internet woodworking community so I did that more or less for free. What goes around comes around. It's just turning a few top hats.

In the first category - people who approach me - my experience has been mixed. At one extreme was a chap who wanted a camera mount made, rewarded me with a bottle of wine and was happy because the commercial item would have cost £75. I didn't know that! At the other end I made a VMC riser for someone who paid more than I'd asked and complimented me on my machining. I guess he knew what went into getting it all set up and accurate.

I've gained experience [and a (very) few quid) ] by doing stuff for other people, but I have no commercial ambition. I confess that I was actually slightly relieved when it looked like I didn't have to make another handwheel - been there, done that ,but it seems it's still on. I asked £45 - is that reasonable do you reckon?

I think I should probably tend my own garden. Thanks (largely to this forum) I think I have developed the skills to do what I want to do and have fun, for the the time being at least.

Robin

That resonates Jon - echoing the reason for my post perhaps. How long should it take.

Robin

Edited By Robin Graham on 19/06/2021 02:48:04

Edited By Robin Graham on 19/06/2021 02:48:44

Title is a bit vague - how long is a piece of string (longer than you think!), so I'll give a particular case.

A while back I was approached by a woodworker who had who had acquired a Kity table saw which he was thinking of scrapping because the moulded handwheel which controls the rise/fall and tilt of the blade had failed:

It's a bad design because the nylon (I think) gear meshes with with a steel rack cut in the pressed steel housing of the machine, with a predicable result.

I made a replacement in steel which involved measuring up the original, drawing it out (in my primary school way):

and making a new one in steel:

It's straightforward enough lathe work, but I have no realistic idea of how long it took because I am quite disorganised.

I suspect that I am slow - perhaps it took me 2 or 6 hours from start to finish. Maybe more!

I'd be interested to know how long this would take others using manual machinery. In my head it was "Half an hour mate, stick a lump of 3 1/2 inch in the chuck, twiddle some handles, bung it on the mill, drill and tap a few holes, job done." But of course it isn't really like that.

Robin

Edited By Robin Graham on 13/06/2021 01:27:33

Edited By Robin Graham on 13/06/2021 01:44:04

Weirdest one I ever had was typed message, delivered by snail mail and postmarked Nottingham, informing me that my uncle Hubert Graham had sadly met his maker (it was tragic accident) in his travels across China. His estate amounted to about $1m and would be passed to me for the asking. It somehow slipped my mind to claim the money, But no problem! Six months later I was told he had unfortunately suffered yet another fatal accident, but in the interim his estate had grown to $1.5m. He always was a reckless chap old Hubert, having fatal accidents all the time, but he knew how to make money, even when dead.

Robin Gra-haam.

Hmm. Can you explain that further John? If it's right I'm back to square one in trying to understand this. Assuming the tool is dead centre at the headstock end and travels parallel to the spindle's rotational axis I can't see how it gets closer to the rotational axis at the vertically displaced tailstock end than it was at the middle of its travel.

Robin.

Edited By Robin Graham on 07/06/2021 01:31:17

Thanks for replies / discussion. I posted about this here because I was reading this forum before retiring to bed, and the thing was still festering in my mind. I had perhaps imbibed a Talisker too many, and wanted to let off some steam. An unwise posting policy!

I wasn't intending to spark a debate about charities - I contribute to a few on a regular basis, have worked with REMAP contributing time and materials, and have no problem with all that. It was more about the near criminality of this approach on my doorstep and my inability to identify and resist. We actually had a minor tug of war with a £20 note. But how do you know if it's someone genuinely trying to get out of hole, albeit by trying to dignify a request for charity by cloaking it in the guise of mutually beneficial commerce, or a scalper?

I was once approached by a guy who asked me for 20p towards a cup of coffee. I really had no change, and told him I had nothing smaller than a tenner. No problem, he dug in his pockets and diligently counted out £9.80 change. I doubt that it was actually a cup of coffee he was after, but it made me smile and he was 20p closer to a wrap. I'm OK with that - it was an honest transaction, he knew that I knew it wasn't about coffee.

Robin.

I answered the door last night to see a chap with a bag over his shoulder and a beaming smile on his face. Right, I thought, I'm going to have to pay £5 for a few J-cloths. I don't mind doing that if it's a way to help people in trouble. But this guy just kept trying to stuff useless junk into my hands - I think he thought that if I'd touched it I'd bought it. It ended up with me agreeing to buy two items for 15 quid (2 quid at the pound shop, but hey-ho I'm being charitable).

I had nothing smaller than a £20 note - he grabbed it from my hand and said that unfortunately he had no change. I didn't entirely believe that ,said that the deal was therefore off and attempted to retrieve my money - these new polymer notes are fairly strong, but I didn't want to tear it and gave in. He then scrabbled in his pocket and found £2 which he offered for change. I said that I was trying to help him, but he wanted to steal from me and I wasn't having it , whereon he produced a fat roll of cash and peeled off a fiver.

It left a bad taste - I'm happy to help genuine charities or individuals in need where I can , but shan't fall for this again. It's not the money, it's just having been a sucker which stings.

Robin.

Edited By Robin Graham on 05/06/2021 23:37:46

Edited By Robin Graham on 05/06/2021 23:39:50

Edited By Robin Graham on 06/06/2021 00:18:10

Thanks for replies - it seems that my analysis is right. I confess that, like Bo'sun, I thought off-centre was off-centre whatever the direction until I put pen to paper and tried to work it out.

I think that if the formula I derived [I arrived there by discarding terms O(delta_h^4/R^2) and above] is correct I have the answer to my question about the profile of the taper which results from vertical misalignment. The deviation delta_h of the tool path from the rotational axis of the work is linear in Z, the distance the tool has traveled, so delta_R is quadratic in Z, ie the taper is parabolic, in contrast to the linear taper from horizontal misalignment. I think!

Thanks again, Robin