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Member postings for Robin Graham

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

Thread: How long does it take to make things?
24/06/2021 23:53:15

Posted by SillyOldDuffer on 19/06/2021 12:27:57

...

Back home, I wasted another couple of hours debugging a computer maths problem which turned out to be a bleeding obvious beginner mistake. (BODMAS!) It's because I flit between jobs, never mastering anything. I can do electrics, plumbing, woodwork, tiling, gardening, fix cars, and cut metal: none of them well!

...

Dave

 

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:

offeringgear.jpg

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:

kityspindle2.jpg

 

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,

kitywheel2.jpg

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

19/06/2021 02:38:45

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

Posted by Jon Lawes on 14/06/2021 10:57:26:

When I was an auto electrician I used to price a job on how long it should have taken rather than how long it took bearing in mind I used to faff to try and make it perfect.

I wasn't a very good businessman and I don't do it anymore.

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

13/06/2021 01:23:46

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:

kitywheel2.jpg

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):

kityhandwheeldrawing.jpg

and making a new one in steel:

kitywheelfront.jpg

kitywheelback.jpg

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

Thread: Yet another scam
11/06/2021 23:44:10

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.

Thread: Taper due to tailstock height misalignment.
07/06/2021 01:30:43
Posted by John Reese on 06/06/2021 23:22:05:

When turning between centers vertical misalignment of the tailstock will result in a part that is fat in the middle.

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

Thread: Scalped on my doorstep - it left an unpleasant taste in my mouth.
06/06/2021 23:40:14

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.

05/06/2021 23:34:27

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

Thread: Taper due to tailstock height misalignment.
04/06/2021 22:26:49

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

03/06/2021 23:21:18

This doesn't seem to be a problem for me, but I came across discussions of the influence of lathe tailstock height misalignment on turning parallel between centres whilst looking for other related info. The discussions were initiated by people who had bought a lathe and, by one method or another, had found the tailstock centre to be high with respect to the headstock. The advice from seasoned hands was not to worry - provided the tailstock is OK in the horizontal plane, vertical alignment (unless grossly out) would be insignificant, but no explanation was given. I wanted to understand this better and tried to work it out.

I'm very bad at 3-D visualisation so tried to approximate the problem by imagining that the tool was cutting dead on centre at the headstock and low by delta_h at the tailstock:

tailstockheightcalc2.jpg

After a bit of algebra it came out that the radius at the tailstock end would be the radius at the headstock plus the square of the distance of the tool under centre at the tailstock divided by the diameter of the work at the headstock.

If this is so, it would explain to me why vertical alignment is relatively unimportant - on a nominal 10mm diameter workpiece, even if the tailstock were 0.1mm high it would lead to a discrepancy of 0.1x0.1/10 = 0.001mm on radius.

I'm not sure that I've set the problem up correctly though - I've a sneaky feeling that I've over simplified, and conic sections or something come into it. The intersection of a plane with a cylinder can be an ellipse, so maybe turning with the tailstock off-height gives a barrel shape - I just can't visualise it!

I realise that this may have little practical importance at home workshop levels of accuracy, but I'd like to understand it better.

Robin

Thread: Machining a female MT1 taper
30/05/2021 00:11:39

Just to wind up with how it went. The repair didn't work (the spindle was too badly bent) so I reverted to plan A.

I set up to turn between centres:

spindleturning101.jpg

and turned the outboard LH thread and other external features. I was pretty happy to find that (according to my Sunday Best Mtitutoyo mic) the parallel section was indeed parallel to 0.002mm over 100mm.

Because I had no easy way of doing the spring-loaded dog thing, I turned the work round, set it in the 4-jaw and centered on the bearing seats by fiddling with the chuck and the steady arms:

spindle102.jpg

I then parted off the stub at the tailstock end (yes, I did take the tailstock off before finishing the cut), drilled, bored and reamed the internal taper and cut the RH thread with this setup.

The finished spindle:

nearlydone.jpg

has ~ 0.01mm TIR on the internal taper with respect the the bearing seats. OK, not great but not too bad.

I nearly had a heart attack when I spun up the (commercial) drive centre and saw the spur point wobbling visibly - but it turned out the commercial part was at fault. I guess it really doesn't matter so much with woodturning,

Many thanks for advice - I've learned a lot from this project, simple as it may seem to many of you.

Robin.

 

 

 

Edited By Robin Graham on 30/05/2021 00:13:13

Thread: Lathe run out
25/05/2021 23:53:29

Robin, I have a very similar lathe, albeit Axminster branded. It sits on the wonky flagstones of a 200 year old cellar, using eight (four per pillar) 80mm diameter rubber feet on M12 studs (I got them from WDS I think):

lathefeet.jpg

I was lucky enough to have to have the generous help of a professional engineer (the late John Stevenson) in setting the machine up. He spent half an hour muttering, twiddling the nuts and checking the ways with a level before announcing 'that's good enough'. No shimming or anything like that, and it was indeed 'good enough' - it turns parallel between centres to < 0.01mm over 400mm. The lathe weighs about 600kg, of which I reckon about 100-120 kg is in the stand and the rest in the machine - so it's the tail wagging the dog - but it seems to work.You'll get there! It won't twist after it's been set up properly - at least mine hasn't.

Your method of projecting the spindle axis by holding a piece of what looks like rolled BMS in a 3-jaw is, unfortunately, not good . For starters, the bar cannot be relied on to be round/straight and the chuck won't hold the bar dead on axis anyway. Then there's gravity. You need to think about what exactly you're measuring and why. And re-read what others have said upthread.

Another Robin.

Thread: The worst 'upcycling' tragedy ever?
23/05/2021 23:47:15

I don't get out as much as I'd like these days (for obvious reasons) , but on a recent expedition I spotted this in the window of a new shop in my town:

upcyclingtragedy.jpg

I'm not sure where to start with the badness, but I'll have a go.

  1. If they've gutted a working Wolf drill to make this monstrosity it is, if not a hanging offence, at least worth some sharp words from the bench.
  2. If the drill was unrepairable (unlikely - they were were built to last) the stand would still be be useful - it looks well made.
  3. Even as a piece of retro-industrial art it's a piece of dritt, as they might say in Norway. I don't want to use inappropriate English language and be censored.

The shop was closed when I passed so I couldn't ask what they wanted. I'll be down the town tomorrow and inquire, if it hasn't been snapped up.

Anyone want to guess the price , or give other examples?

Robin.

 

 

Edited By Robin Graham on 23/05/2021 23:59:57

Thread: Machining a female MT1 taper
16/05/2021 23:22:36

Many thanks for taking the time to post those pics John - much appreciated. Often I am either confused by technical explanations (too hard) or frustrated by over simplifications (too soft), but the level of the text you reproduced is pure Goldilocks for me. Obviously I'm 100 years behind the times.

It turns out that the spindle in question was knackered by an over-enthusiastic attempt to remove the original bearings, and the damage is limited to the threaded portion to the left of the flange in my earlier pic. In which case I might be able to fix it without having to make a new spindle. Shucks, I was looking forward to the challenge. I might have to do it anyway, just because I think I can.

Robin.

Edited By Robin Graham on 16/05/2021 23:25:34

15/05/2021 00:09:54

Thanks for further suggestions. I think I now have enough to be going on with with - I have plenty of 1" scrap to play with, so shall try various things in the hope that when I get to the job proper I'll have a rational 'schedule of operations' (I've learned some new vocab there!) worked out and get it right in one go.

NDIY - I am planning to buy a MT1 soft arbor if only to line up the topslide for initial boring (I don't have any MT1 tooling) , so good to hear that you have found they can be useful for between centres work.

John - many thanks for the illustration and accompanying text. That's very useful. Can you give a reference? I want to see Fig 28! And where does the universal grinding machine (I haven't got one) come into the story I wonder?

The manufacturer (Nu-Tool) of the lathe supplied a nut to fit on the threaded nose of the spindle - the idea being that unscrewing the nut will eject the centre. I don't understand why they also made the spindle hollow, but I could drill it through if there is good reason.

Hopper - you are right - for a woodworking lathe it's not worth chasing tenths. But maybe someday I'll want to make a precision spindle or a precision something else, and this experience will be useful. So I want to get it as good as I can. I take your point about the centre disappearing down the hole - I shall tread softly.

Robin.

14/05/2021 01:17:31

Thanks for replies. Obviously many ways to skin this cat - sadly I won't be able to use John Pace's grinding technique because - well, I can't. Looks like a nice way if you've got the kit though! The idea of a making Morse taper boring bar is interesting - I could probably do that.

I've now bought the tools pictured in my opening post though (only one remaining, order within 39 minutes for next day delivery - I'm a sucker for that sort of sales pressure) so shall experiment with them bearing in mind advice about achieving concentricity.

I'm sure I can make the spindle to acceptable tolerances one way or another, but I'm going through a 'get it right first time man' phase. I'm bad at planning lathe machining sequences to avoid resetting the work, losing concentricity and having to resort to the 4-jaw though.

This is the spindle I want to reproduce:

lathe spindle-1.jpg

 

The internal 1MT taper is on the left - the rest of the spindle is solid. My thinkings so far, based on the kit
I have are:

  1. Mount an oversized bar between centres, turn the external features then remount on-axis in the 4-jaw to make the taper.
  2. Make the taper first in oversized bar, put a small 60 degree chamfer at the end, mount between centres and then do the external features.
  3. Make the taper in oversize bar first, bung in a 1MT soft arbor and rely on the centre hole in the soft end of the arbor to turn the external features between centres.
  4. None of the above sad

It's for a wood turning lathe, so a couple of thou out isn't going to be a problem, but I want to get it as accurate as I possibly can - I took the job on for a small, but negative, financial gain as a way of advancing my skills and doing someone else a bit of good.

Robin.

 

Edited By Robin Graham on 14/05/2021 01:18:58

Edited By Robin Graham on 14/05/2021 01:27:37

Edited By Robin Graham on 14/05/2021 01:36:01

12/05/2021 02:07:44

I've been asked to make a spindle with an internal MT1 taper. I'm pretty sure that I can do it, at last resort by trial and and error with a slender boring tool, but it's a challenge because MT1 is only ~ 9.4 mm at the thin end and about 54mm deep. It'd take a long time and much blue (Stuarts and language) I expect.

Looking for an alternative approach I came across these reamers:

mt1reamers.jpg

The top one is 'roughing' and the other finishing. But I don't know how they are meant to be used. Could I get away with step drilling or boring, then use the rougher to take off the corners and finish with the other? They are cheap Oriental offerings made from carbon, not HS, steel, but it's a one-off in EN1A so maybe it could work.

Has anyone used these tools and can advise? Or any suggestions for other methods?

Robin.

 

 

 

 

Edited By Robin Graham on 12/05/2021 02:17:04

Edited By Robin Graham on 12/05/2021 02:22:13

Thread: First attempt at trepanning.
09/05/2021 22:29:13

Thank you Jason and Nigel for further info. Some more ideas to try - as I have several to do it is worth my time experimenting to get this technique under my belt. Apart from the pleasure of learning something new!

In my first (successful) attempt I went through until I saw a bit of a bulge emerging on the back of the work, then turned it over and took off the bulge with the trepanning tool. I then knocked out the centre piece and finished by boring. I can see that trying to go all the through without a centre support as Nigel suggests would be a surefire recipe for disaster.

Thanks again for all the suggestions , Robin.

09/05/2021 00:08:14

Thanks for replies. I confess that I didn't think this through too well - I just ground a 4mm square bit with enough clearance on the outside edge. As I (sort of) got away with it the first time I thought, pending arrival of a more suitable piece of HSS, I'd try another disc and experiment with speeds and feeds. The tool broke.

I haven't got Mason's book, but Andrew's comment that the tool should be half the width and twice the height (ie 2mm wide by 8mm high) made me think - surely that would foul on the outside edge? So I calculated:

trepanningformula.jpg

 

It seems that for my 100mm hole a 2mm thick by 14mm high tool in that geometry would (just!) clear if I've got it right. Obviously that might not be the optimal tool geometry, it was just to give me a starting point. If any kind soul has a pic of Mason's tool shape to share, that would be interesting.

Hopper - I had to read your point about the notch about six times, but I think the penny has now dropped. Possibly!

Robin.

 

 

 

 

 

 

Edited By Robin Graham on 09/05/2021 00:10:16

Edited By Robin Graham on 09/05/2021 00:11:46

06/05/2021 23:49:53

I have a job which involves making 100mm holes in 150mm x 6mm discs of black plate:

150mmring.jpg

As I have a few to do, and the cutouts would be more useful than a bucket of swarf, I thought I would have ago at making a trepanning tool.

As you can see, it worked - but there is room for improvement.

I made the tool from a piece of 4mm square HSS:

treptool02.jpg

treptool01.jpg

treptool03b.jpg

I locked top and cross slides and fed manually using the saddle handwheel. Spindle speed was 65rpm giving ~20 m/min cutting speed.

What I found was that sometimes the tool chattered with a low grumbling sound, sometimes it squealed, and sometimes it went like a hot knife through butter. The discs were bought off eBay so I don't know how consistent the metal is, but my gut feeling is that the variation in behaviour was more likely to do with my inability to maintain a steady feed - especially as I've never done this before, so was perhaps overly hesitant. Something I've learned about parting off is that hesitancy is not good!

If so, I suppose power feed might be the way - but I have no idea what feed would be appropriate.

Or maybe the tool geometry is wrong. I used 4mm square because I had it - but perhaps that's not rigid enough and I should be using rectangular section, more like parting tool geometry.

Sorry that this is a bit rambling and unfocused - any education about this technique would be most welcome.

Robin.

Thread: Protective film for polished metal.
05/05/2021 00:11:50

Thanks for suggestions.

I had tried clingfilm - I couldn't get it to stick reliably. It is also quite thin at ~ 10μm.

I've used Renaissance wax for metal finishing, and it's good stuff I agree - but not really what I want here. Corrosion isn't the problem, it's a need to protect the work from the scratch demons which seem to inhabit my workshop. Or to put it another way, to protect the work from my sloppy and inconsistent practices.

I have MetalGuard from ARC - it's great for what it's meant for, but it's not what's needed here.

I had thought about painting or spraying with some sort of protective film, but then it has to be removed with a solvent, which would give further scope to the scratch demons.

It sounds like the vinyl transfer tape which Adam suggested might work. I had a look (I wasn't aware of the technology) and have ordered a roll. I went for the brand which had the most negative reviews for the intended purpose - 'not sticky enough'. It won't need it to be in place for more than a few days,

Many thanks to Pete and Adam for offering samples - very much appreciated, but I succumbed to the lure of 'Free delivery: Tomorrow. Order within 14 minutes'. So the stuff should be with me tomorrow - or later today, looking at the clock now.

Robin

Edited By Robin Graham on 05/05/2021 00:13:55

Edited By Robin Graham on 05/05/2021 00:14:43

Edited By Robin Graham on 05/05/2021 00:35:32

Edited By Robin Graham on 05/05/2021 00:50:23

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