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Member postings for SillyOldDuffer

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

Thread: Recommend a grade of steel
25/09/2021 10:24:40

Posted by Robert Smith 24 on 25/09/2021 08:13:08:

...

The pin was hard and fractured at the shoulder of the 2BA thread and 1/4" pin.

Sounds like a classic fatigue crack caused by shoulder acting as a stress raiser. Best to avoid sharp transitions especially where heat-treatment is applied too: on purpose or accidental tempering is liable to cause micro-fractures, and these are particularly likely to occur at sharp transitions. Parts become much weaker than they should and are very liable to fail when stressed repeatedly.

In this example one side of the groove is chamfered to relieve stress leaving the other side seriously weaker.

relief.jpg

So manufacturing defect(s) rather than using the wrong steel.

Watching 'Forged in Fire' on telly two knives made with saw-backs both failed catastrophically at the first tooth when the blade was whacked into a 4" chain: no stress relief at the teeth and a hefty blade about an inch deep broke...

Dave

Thread: cutting spur gears on a mill
25/09/2021 09:52:15

Posted by Andrew Johnston on 24/09/2021 20:15:58:

...

Spur gears are simple compared to other types of gear. Gawd help us if we ever get onto other types of gear!

Andrew

These examples are from FreeCAD's 'Gear' Workbench, which may be downloaded from Tools->Addon manager.

1. Involute and Cycloid side by side: although the difference isn't obvious these two gears don't mesh properly:

gearinvcyc-0.jpg

2. Bevel Gear:

gearbevel.jpg

3. Crown Gear

gearcrown.jpg

4. Lantern Gear:

gearlantern.jpg

5. Timing Gear

geartiming.jpg

6. Worm:

gearworm3.jpg

7. Hypocycloid gear.

gearhypocycloid.jpg

The hypocycloid form, with or without pins, is a new one on me. Looks hard to make - anyone know what they are used for?

Dave

Thread: Back to Imperial
23/09/2021 11:12:12
Posted by Robin on 23/09/2021 09:56:43:
Posted by Jon Lawes on 23/09/2021 05:29:42:
Posted by Peter Greene on 23/09/2021 01:49:34:
Posted by Robin on 21/09/2021 10:14:21:

...

...

...

I feel your pain. Unlike Gerber, AutoCAD defines an arc by angles rather than by end points, Stray from the cardinals and nothing quite fits sad

Is that true? In my youth I failed to get on with AutoCAD because it had so many features that I didn't have time to explore, but many people rated AutoCAD highly. I found it difficult to navigate. Now I happily use QCAD for all 2D plans. Although simpler than AutoCAD, QCAD has ten different ways of drawing arcs only two of which require angles. I'm surprised AutoCAD doesn't do much the same: possibly other arc options are hidden behind a sub-menu?

I remember reading an article about AutoCAD in MEW or ME where the author reported lines not joining. I wondered if he was driving AutoCAD wrong, either by not selecting the right tool, or not setting the appropriate snaps. The latter are important and not always obvious.

Dave

Thread: cutting spur gears on a mill
23/09/2021 10:50:07
Posted by brian jones 11 on 23/09/2021 04:08:55:

In 1890 they knew a thing or two and armchairs hadnt been invented

https://books.google.co.uk/books?id=dyYJAAAAIAAJ&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false

I see not having an Armchair has let Brian down again. Having found a copy of the most excellent Grossman's Lessons in Horogogy, he hasn't read it! The Grossmans, father and son, were scientists. They say:

grossmanquote.jpg

Note the bit about the practical workman faithfully following 'the principles' in the execution of his work!

Armchairs as tools are valuable at the design stage and when things go wrong. Not necessary for repetitive work or following instructions. Interpreting a good drawing is quite easy; bad drawings stretch the poor old brain, which might need help from strong coffee or this forum!

Actually, the armchair isn't the best thinking tool available. I prefer a comfy office chair in front of a well-lit desk equipped with a computer, notebooks and pencils. At first the computer is used as a support tool rather than a thinking aid: they're good for reference; calculations; formal write-ups, and exchangeing ideas with friends etc. I learn best on paper taking notes from printed textbooks and start designs with rough pencil drawings rather than going straight to CAD. The computer is good later on at formalising and validating ideas, often exposing mistakes and allowing them to be corrected without too much aggravation.

Some problems are best thought out whilst walking, and I occasionally wake up with answers, presumably having processed them subconsciously overnight whilst asleep or doing something else entirely: like free-hobbing the 'not thinking about it' method can't be relied on though!

Going back to free-hobbing, a single gear, no matter how good looking, is useless. The acid test is making two or more gears that mesh together between designed centres. Free-hobbing struggles to do this and understanding why free-hobbing fails is an armchair job. No need to read Grossman, most shortcomings have been covered in this thread.

While free-hobbing isn't good engineering, Brian is congratulated for flushing out other methods of making gears. A thread that gets over 240 replies and 12000+ reads can't be all bad!

smiley

Dave

 

Edited By SillyOldDuffer on 23/09/2021 10:52:30

Thread: What do you think of this con
22/09/2021 16:49:51
Posted by Bazyle on 22/09/2021 13:15:44:

I think Trading Standards require the marked price to be honoured even if wrong ...

Not my understanding at all, though lots of people believe it. For a contract to be binding there has to be an 'offer' and an 'acceptance' by both purchaser and seller. How would you feel about a legal obligation to honour offer prices if your house was accidentally advertised with a zero missing off the end?

When a customer offers to pay at the till, the store has no obligation to accept. Stores can and do turn away customers away who appear to be underage, drunk, mentally ill, or are not legally entitled to buy the item.

To avoid being accused of conning customers, many UK stores do honour mistaken asking prices. It's voluntary though - they don't want to upset customers! In Old Mart's case I'm sure BrianG is right: it's illegal in the UK to sell alcohol for less than the duty + VAT price.

Mistakes can cause tricky problems. On a Contract Law course years ago we were told about this example. A Scrap Dealer bought a large number of wooden Stirling submachine gun boxes at a Government Surplus auction. At his warehouse he discovered about 20% of the boxes contained brand-new submachine guns. These he offered to sell back to the government at market rate. Ended up in court. The scrappy's position was he'd bought the boxes legally at an auction, the contract was fulfilled, and he was therefore entitled to sell whatever the boxes contained. The Army said the scrappy couldn't own or sell sub-machine guns because he wasn't a licensed Arms Dealer: therefore he should give them back before they threw the book at him. Scrappy pointed out it was illegal for the government to sell the guns to him in the first place. A right mess! Unfortunately I was sent home due to illness and never found out how it ended, but due to a mistake both parties had broken the law expensively.

Ought to explain for the benefit of US friends that possession of just one automatic weapon in the UK is a serious matter. British subjects have no constitutional right to bear arms which makes it much harder for our nutters to organise mass-shootings. And taking a hard line on the private ownership of firearms hasn't undermined democracy.

Dave

Thread: Back to Imperial
21/09/2021 18:05:57
Posted by Nigel Graham 2 on 20/09/2021 21:47:00:

...

The Crown mark on a beer glass does the same as the CE mark - shows the glass has been manufactured to its appropriate weights-and-measures standard.

...

Pedant alert!

Alas not!, the beer glass Crown was an Excise Mark, confirming the capacity of the glass for both customer and the Government. CE is a conformance mark: sellers add it to assert the item meets relevant EU standards, which are usually safety related.

Provided it's honest, CE assures the customer the item is safe to a standard acceptable in all European member states. Governments don't care much about them. In sharp contrast, the crown mark was only valid in the UK, and the Crown cared very much! It was a reminder to the trade that alcohol was taxed. Customs and Excise made rigorous checks and had more extensive powers of entry than the police and inland revenue. Avoiding excise duty was a serious criminal offence, and the government dropped like a bomb on offenders. Being an offence against the crown, expect the maximum penalty!

Crown and CE Marks have nothing to do with quality. The beer in a Crown glass was often a bit 'off' as I remember, but once sold, then tax is payable. Likewise, CE marks can be stamped on rubbish, and there's no come-back as long as it's safe. And even if the item is hazardous no action will be taken unless Trading Standards give it priority, which is unlikely because they've all been slashed back since the 1970's.

These days the crown mark is unnecessary on glasses because pumps are calibrated for tax purposes. Putting Crown Marks on glasses now has no meaning other than nostalgia. About as daft as my local herbalist, who once claimed their shop to be a 'Nuclear Free Zone'. Yeah right!

Dave

Thread: Making milling vise jaws
21/09/2021 17:09:05

I'd say mild-steel is suitable for a first attempt, in fact a decent beginner challenge. I fitted plain mild-steel jaws to my Record Vice №4 in preference to its hardened originals because they tended to mark the sort of work I do. I also made aluminium faces for more delicate work, but buying a pair of fibre jaws was a waste of money: not used them yet.

I consider my mild-steel jaws to be disposable, because they do slowly ding up as David George describes. How long it takes to knacker a set of jaws depends on the volume of work done and how brutal it is. If mild-steel isn't good enough, you could case-harden it, or switch to gauge plate, or one of the tough steels; beware - tough steels can be a pain to machine, which is why gauge plate exists. The other big advantage of gauge plate is it is ground flat and parallel, important on a machine vice. Bright Mild Steel isn't so accurate, but my experience of of bits cut from the same rolling has been good enough for most purposes.

As to the sizes, jaws are usually slightly wider than the vice and deep enough to close without putting the screw to end-of-travel. What you suggest sounds right. One trick is to knock up some jaws in wood or cardboard and test them for fit, opening and closure before spending time and money on a potential misfit in steel. Once confident the template is the right size, then make the real one.

Provided they are parallel there's a fair amount of latitude in jaw making so don't worry too much. Might even be an advantage make your own - fit taller jaws or cut Vs in them to holding round stock.

I take it the vice was second-hand? If so don't be afraid to scrap it if it's poor condition: missing jaws may be the tip of an iceberg because vices are often badly abused. Get rid if it doesn't grip properly: jaws lifting badly or not parallel; twisted frame; rocking; worn screw / nut, or other obvious defects. Perfection isn't essential - quite often lifting can be fixed by tapping the work down with a mallet - but a machine vice that allows work to move or won't grip straight is a pain in the proverbial.

Dave

Thread: cutting spur gears on a mill
21/09/2021 16:22:51
Posted by brian jones 11 on 21/09/2021 13:33:18:

Well if a cutter like that had a helix?

...

A helical rack cutter would grind off all the metal leaving zero teeth, because the blank isn't free to rotate. However, no teeth at all still meets Brian's extremely low Statement of Work - push two plain wheels together and it's a friction drive!

Dunno what others think, but I score free hobbing at one out of ten. Thumbs down because the method's many limitations result in gears that are unacceptable for most practical purposes.

As H L Mencken said: 'For every complex problem there is an answer that is clear, simple, and wrong."

Dave

Thread: Not enoughh CO2 ?
21/09/2021 09:55:04

Posted by not done it yet on 21/09/2021 09:03:34:

...

How more stupid can the human race get?

...

No need to be more stupid than we already are! Give up energy today for reasons I don't understand? Party on, and sod the consequences. And anyway, as we'll all be dead before the result of burning gigantic quantities of fossil fuels gets really bad, there's no reason for silly old duffers to change.

All you have to do is denounce 'Greens', 'Tree-huggers', scientific consensus and all the evidence that anything is wrong. Unfortunately the evidence of climate change is still quite subtle, and many people won't believe it until they are personally effected. Central London flooded twice in 10 years might do it, and the probability of it happening is rising!

Thing is humanity are plain bad at assessing risk. This is true even when people understand the problem, and worse when there are vested interests. When it comes to risk we are all thickos, but some are thicker than others. Some people really believe the world is flat, and the moon landings were faked, and that Stalin was an Uncle Joe.

Dave

Thread: Stuart Twin Victoria (Princess Royal) Mill Engine
19/09/2021 10:22:33
Posted by Dr_GMJN on 19/09/2021 07:47:40:

... noticed it had an oiler on the cover as well:



It seems to have two taps, perhaps so you can oil during running. Are these available for models?

...

No idea if they're available for models.

According to my book, this type of lubricator is called a Cylinder Oil Cup, or Tallow Cup, depending on whether the lubricant is oil or tallow. "Made of Gun-metal, upper cock for filling; lower cock for admitting the oil or melted tallow to the cylinder or steam feed pipe. The steam carries the oil forward to the piston and valve."

Although it looks similar to an ordinary Oil Cup, Tallow Cups work on a different principle. This type of lubricator runs hot enough to melt tallow, and it adds oil to steam, not drip feeding a bearing like an ordinary lidded Oil Cup. Two valves are necessary for refilling on a Tallow Cup because the lubricator's output is normally at steam pressure; opening both valves with the engine running would blast the operator with a jet of oily steam. Potentially dangerous on a full-size engine.

Does anyone still use tallow as a lubricant these days? Being rendered animal fat makes it liable to go off and become a smelly bio-hazard, but it has both grease and oil properties. Grease is best for slow moving joints, as when a steam engine is started from cold, and oil is best when an engine is running hot and fast.

Absence of smelly tallow is another reason I suspect visiting a heritage steam engine can't be fully authentic. Apart from the H&S precautions, the engines are too clean and brightly lit; many are turned cold by an electric motor, and if the engine is being steamed, the boiler burns clean coal or coke. The visitor doesn't experience the heat, hard work, long hours, or dimly lit stink of an actual industrial engine earning a living.

Dave

Thread: Old gear
18/09/2021 21:38:27

Posted by Derek Lane on 18/09/2021 20:51:29:

...

I know that many say try and use known metals from a reliable source but this just seems too good to throw in the scrap bin

I'm against beginners trying to learn on random scrap because it's so hard to tell if any resulting problems are due to them, the lathe, or the material. New boy abandons fun hobby on day two because his new mini-lathe run at the wrong speed fails to cut a nasty lump of scrap work-hardening stainless steel!

As gearwheels have a hard life, it's quite likely the metal is tough as old boots. So don't blame the lathe or yourself if the gear turns out to be nasty hard stuff that won't cut properly. May be necessary to experiment. In this case there's nothing to be lost by trying. Go for it!

Dave

Thread: Auto-Oiler replacement for Myford and other drip oilers.
18/09/2021 14:10:00

Gold star deserved for providing GUI software making it easy for the user to configure the Arduino. Must have been as much work as developing the Oiler itself!

Overcomes a user hurdle, which is the chap who needs to modify Arduino configuration settings without having to learn the Arduino Editor and IDE first. I don't recall seeing another Arduino project that went the extra mile on this problem.

Dave

Thread: Back to Imperial
18/09/2021 11:12:47

Looks like classic gesture politics to me, definition: “any action by a person or organisation done for political reasons and intended to attract public attention but having little real effect”.

The source follows the Final Report of the Taskforce on Innovation Growth and Regulatory Reform. The second phase of this is the proposal "Brexit opportunities: regulatory reforms" This is essentially the bullet list:

  • Reintroducing the Crown Stamp (on pub glasses)
  • Dematerialisation of shares
  • Digital Transformation of Regulation
  • Review EU restrictions on selling in pounds and ounces - We will review the EU ban on markings and sales in imperial units and legislate in due course.
  • Specification for the Sharing of Underground Asset Data
  • Expand access to property attribute data held by the Valuation Office Agency -
  • Digital driving licences, test certificates and MoT testing
  • General Aviation Reform
  • Heavy Vehicle MOT Reform
  • Aviation Consumer Policy Reform
  • Transport Sandboxing
  • Modernising diabetes management for lorry and bus drivers
  • Repeal of the EU Port Services Regulation
  • Ofgem Strategy and Policy Statement (SPS)
  • Offshore Network Coordination
  • Medicines and Medical Devices Act 2021
  • Software and artificial intelligence as a medical device
  • Reconsider regulations to allow the spraying of plant protection chemicals from drones
  • Electronic Trade Documents when buying and selling internationally.
  • Execution of Documents
  • Environmental Licencing and Permitting
  • Promote a flexible, market-based trading system for biodiversity offset credits
  • Digitalisation of Export Health Certificates, Imports, and Trade

All to be introduced 'in due course' and not all of it EU related. To find out what's actually going on I recommend reading the actual documents rather than relying on newspapers, sound bites or bar room opinion. Having inspected the detail, is your government delivering what you expected? If not, tell your MP!!!

Dave

Thread: cutting spur gears on a mill
16/09/2021 14:42:28

Posted by brian jones 11 on 15/09/2021 22:27:24:

...

I dont know of a simple system that allows you to cut gears with ease and speed (I am discounting the modern use of stepper motors for the job for the purposes of this discussion. No electronics allowable

...Hence my pursuit of a cheap charlie way of knock up spur gears ...

But Brian, you should know of a simple system! I've mentioned it at least twice in this thread, provided a picture, and linked to Neil's Orrery Thread where he used the method to make many gears.

On the 20th August, I typed:

Using a tap to cut gears isn't new. I've experimented with it, but got much better results with a Sunderland Rack cutter and Rotary Table:

dsc03599.jpg

Neil Wyatt made a lot of gears this way for his Jovilabe Orrery a few years ago.

Unlike a tap, Rack Cutters get the number of teeth right and, with a little care, they cut an accurate involute. Rack cutting and Hobs do take longer!

Boils down to how much the operator needs an accurate gear as opposed a quick approximation. If gashing gears with a tap is 'good enough' for the job in hand, go for it! No-one objects.

The much despised armchair is a valuable engineering tool. They're good for research and thinking.

Is Mr Sunderland's method too complicated? It requires a:

  1. Lathe and V cutter ground to turn the Sunderland Rack Cutter
  2. Mill, milling cutter and horizontal rotary table (or other indexer) to relieve the Sunderland Cutter. (Could be done with a file.)
  3. Mill with horizontal rotary table or other indexer, plus chuck to hold the gear blank.

The results are predictable. This home-made gear has the right number of teeth, it sits on ½" Meccano centres, and it meshes with the commercial plastic gear without shredding it:

dsc03598.jpg

Hobbers are preferred for mass-production because they churn out well-made standard gears quickly and efficiently. Sunderland is mostly used by industry to cut big bespoke gears, often by planing, but same principle.

Sunderland is slower, but there's no need to make a special hob, and it's possible to generate accurate involutes. The Sunderland method can be created in a small workshop without too much trouble, no pre-gashing is required, and results are reliable and predictable. I'd expect Sunderland to be faster than Brian's free method in practice because Sunderland produces fewer rejects. Sunderland wins whenever the centres, or exact number and shape of teeth matter. Sunderland versus Hob is a different debate!

Dave

Thread: Post Office Deliveries
16/09/2021 11:27:53

Curiously, here in Zummerset, the postal service mostly improved during the worst of the Covid crisis in that deliveries arrived at 10am rather than lunchtime, and sometimes on Sunday too! Pure luck. My sister in nearby South Gloucester suffers frequent delays. She knows a postman well: he says the difference is mostly caused by the sorting office: my postal area has a spacious modern facility, hers is old-fashioned, due to be modernised, and the cramped together staff have all been ill.

I don't know how the Post Office are dealing with staff shortages due to Covid, which is still causing considerable trouble. I imagine they recruited lots of temporaries who will be laid off as the situation improves. This laying off may be the source of Social Media comment, though I'm sure the PO (as a private company) is always actively seeking to improve efficiency, and not necessarily in customer friendly ways.

Also in the news is the shortage of HGV Drivers caused by leaving the EU. There are about 600,000 jobs and 100,000 vacancies are causing noticeable delivery delays in some areas. Round here, Builders Merchants seem to be worst effected, plus a few gaps on supermarket shelves, but otherwise no obvious effect on my post, Amazon or other deliveries.

I suspect the impact on deliveries due to COVID and staff shortages depends on where you live.

Dave

Thread: Standard Surveying Thread?
15/09/2021 16:30:26
Posted by Shadow on 15/09/2021 14:43:14:

There are about three different normally used tripod thread sizes. 5/8"x11male, a 3 1/2" male thread and a smaller somewhat proprietary about 5/8" fine female thread.

...

I expensively found by importing an adaptor that the USA 3½" thread isn't the same as the UK 3½" tripod thread...

sad

I'm sure part of the problem is that standard threads are intended for fasteners rather than the screw on fittings found on lens, bottle tops, and proprietary attachments. Reasonable to expect nuts and bolts to match a standard, less likely a camera lens or beer bottle will be metric, Whitworth, or anything else quite 'normal'.

Bet I'm not the only one on the forum who occasionally makes non-standard threads to suit the job in hand. Mine are mostly metric 1.0 pitch on non-standard diameters.

Dave

Thread: Myford ML7 accuracy
15/09/2021 16:09:00

Fingers crossed, as one who has yet to damage his Chinese electronics:

  1. Stop and start the machine with the control potentiometer set to the lowest speed. Banging in and out with the power supply set to deliver high power is asking for trouble.
  2. As hobby machines aren't built for continuous heavy work, best not to take long aggressive cuts. Don't labour the machine or and check the motor isn't getting hot. There's a reason industrial machines are 10 to 20 times more expensive!
  3. Let the machine cut at it's own rate. A bad tempered gorilla in a hurry is much more likely to damage brushes, strip gears, smoke motors, and pop electronics than a skilled machinist. A skilled machinist is also more likely to react to blunt tools, work hardening metals and other mishaps. If the machine isn't cutting cleanly, you may be doing it wrong.
  4. Some early mini-lathes risk swarf getting into the control box via the lead-screw hole. Protect the gap with some sticky tape or a short guard. Later mini-lathes pass the lead-screw through a protective grommet.

Not sure what the relative failure rates are, but note this forum has many posts asking how to fix single-phase motors and duff Dewhursts! Certain older machines are also a bit too delicate for comfort, nonetheless they last for years provided they are treated with respect.

Watched a neighbour using his electric drill on Sunday: won't last, he's far too heavy handed!

Dave

Thread: cutting spur gears on a mill
14/09/2021 11:47:46

Posted by brian jones 11 on 13/09/2021 21:06:20:

...

if i want two gears say 2:1 ratio, stick the blanks of 2:1 OD in your jig and 5 mins later ish you got a result

no fancy hobber linked to spindle ££££, just slice up an HT bolt to suit blank OD/pitch = teeth minus 1

Cheap and cheerful for non ferrous mtl

Cheap and nasty rather than cheap and cheerful! Although it produces teeth, Brian's method is unreliable. It's a good way of producing unreliable gears, which most of us don't want at any price!

Look at Jason's example:

badteeth.jpg

The green circled teeth show the free method 'working', but the nearby red circled teeth highlight a serious problem - malformed teeth. Jason's example wouldn't mesh consistently with itself! Not because Jason is unskilled - it's because the method is flawed.

Having made one plastic gear by this method Brian bravely asserts the number of teeth is OD/pitch = teeth - 1. Maybe, maybe not. The number of teeth produced depends on slip during the cutting process, and it's unpredictable. Half teeth are possible.

The claim that the same cutter will produce 2:1 ratios is untested, and engineers really shouldn't jump to conclusions.

Brian seems keen to sell his idea as a practical man versus Armchair thing. It's not! I suggest others try the method and decide for themselves. Bear in mind the flaws only become obvious when many gears have to fit together. Asking several gears at particular spacings to transmit power or step up with low friction will reveal problems galore. No one has to believe me or Brian, because the method can be tested.

Dave

Thread: Myford ML7 accuracy
13/09/2021 15:09:48

'Lathe for Jewellery Making' changes the requirement somewhat. The purpose implies a small lathe like a Sherline, Taig/Peatol or Cowells. All these are available new. The Cowells is an attractive machine but calls for deep pockets;

In comparison to these small lathes, Myfords are relatively clunky - general purpose, small workshop machines. Certainly not out of the question for jewellery, but a bit clumsy for persistent fine work.

In my opinion the main problem with Myfords is they are overpriced. Chaps rush to pay premium prices for them, even in poor condition. Many Myfords have been lightly used and well maintained by careful owners. Plenty of others have been thrashed beyond economic repair. High prices attract dodgy refurbishers, who periodically cause forum fun when their vile paint jobs and obvious crocks pop up on the web. Best to see second-hand lathes cut metal before buying: remember that a famous brand name on a good looking lathe might be a complete wreck. Being old and British doesn't guarantee reliability - look at the state I'm in!

On the other hand, even well-worn lathes will do acceptable work in skilled hands. This is particularly true of short travel work where a worn bed and wonky chuck don't matter much.

Not sure where the idea Chinese lathes only last a couple of years comes from. Not my experience.

Dave

Thread: CNC Knurling
13/09/2021 14:31:05
Posted by Dave S on 12/09/2021 16:55:44:

...

Got to love the forum smilies in code

Dave

Here's John's code in glorious technicolor, smiley's exterminated:

jhpy.jpg

Couple of small points.

May not make any difference but I would use:

myFile = open( name, 'w' )

rather than:

myFile = open(name,'a' )

'a' opens the file 'name' in append mode, and if name already exists, the new G-Code will be tacked on the end, which probably isn't wanted. The 'w' open() always creates an empty new file so there's no danger of confusing the machine tool by feeding it two or more blobs of g-code in the same file.

Second, again not making any practical difference, John uses format strings mildly inappropriately in his print statements.

print(f"G91", file = myFile)

This is unnecessary:

print("G91", file=myFile)

f"strings" useful for another purpose:

print(f"G01 Z", -1-Z_feed, " F", Z_feedrate, file = myFile)

can be written:

print(f"G01 Z {-1-Z_feed} F {Z_feedrate}", file = myFile)

The second form is particularly neat because formatting, not required in John's program, can be applied to whatever is between the curly brackets.

Dave

PS I like Thonny too.

 

 

 

Edited By SillyOldDuffer on 13/09/2021 14:31:45

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