By continuing to use this site, you agree to our use of cookies. Find out more

Member postings for Robert Atkinson 2

Here is a list of all the postings Robert Atkinson 2 has made in our forums. Click on a thread name to jump to the thread.

Thread: oxygen concentrators
23/05/2020 14:30:46

The other advantges of concentrators for home use is the removal of the safety hazards of high pressure cylinders and stored quantiities of oxygen in the home and and the logistics of supply and transport t multiple users.

Robert G8RPI.

Thread: The sneering detractors
21/05/2020 17:08:37

I Have to agree with Dave (SOD) and Frances. We can't just ignore the bad stuff, certainly not the dangerous. No single person knows everthing or is always correct. Like dave I'm happy to be corrected or enter ino a civilised technical discussion. I probably come over as a bit of a health and safety concerned person, but I've no problem with people setting their own acceptable level of safety as long as it does not affect others. I certainly do things in my home workshop that I would never suggest others do, and some I would not even tell anone I'd done
It is a difficult balance but my view is make sure peopel know that you have concerns and then let them decide for them seves.
I know I frequently annoyed a couple of people on a automotive forum because I would add a "don't forget it's illegal" post to any thread advocating LED replacment bulbs for exterior lights (OK for reversing lights odly) or disabling emissions systems. that didn't make it clear. Similar viewpoint, let readers know the techncal issue and decide for themselves. No need to rant or be rude.

Robert G8RPI.

Thread: Power feed - 'which motor shall I buy'?
21/05/2020 15:57:37
Posted by John Baron on 21/05/2020 14:15:49:
<SNIP>

Hi Robert,

It might pay you to look at how a window screen wiper motor is constructed. That is after you have drilled all the rivets out !

Hi,

I've looked at plenty of wiper motors over many years and fixed more than a few.

The one pictured in your album is typical, Adding a thrust ball to either the pressed steel motor cover or the cast alloy gear case should not be too difficult. Typically its the motor end that has no thrust beraing, typically just a self aligining (bll shaped) oilite type bush. There is normally enough room in the back of the housing to hold a suitable sized ball. A spacer / locator might be required but that's about it.

Robert G8RPI.

21/05/2020 13:29:25
Posted by John Baron on 21/05/2020 10:23:19:
Posted by Robert Atkinson 2 on 21/05/2020 07:40:03:

Why have you got a tumbler reverse gear on a drive from a reversable motor?

Robert G8RPI.

Because the wiper motors are designed to run in one direction only. The worm only has a thrust bearing at one end.

You could just put a bearing at the other end. A single ball for the spindle to thrust on would be good enough. Then you can auto reverse electrically. With tumbler gears you will have to stop rhe motor,move gears and re-start the motor.

Robert G8RPI.

21/05/2020 07:40:03

Why have you got a tumbler reverse gear on a drive from a reversable motor?

Robert G8RPI.

Thread: Used Lathe Pinnacle PL1340C Gap Bed
17/05/2020 09:46:47

A good rotary converter would run about 95% efficency at rated load. Most of this will be fixed lossses such as bearing drag and windage. I woud expect that a 185kW convertey would consume about 1kW off load. However you need to think kVA too because that's what the electricity meter responds to and can be a lot higher for an off load motor

If you are going to be running 3 or 4 5kW machine tools at the same time you should probably get a 3 phase supply. Otherwise modern solid state converters are probably the best solution. You don't HAVE to run a VFD att different frequencies, if you run it at 50 or 60 Hz it will run any machine if the voltage suits the motor.
The issue many have mentoned is getting a "400" volt output. from a 240V input. There a number of ways to do this. Easyist is a solid state converter specified for the task. These tend to be more expensive. As you have a 480V supply and a 3 phase in 3 phase out VFD converts it's input to DC it is entirely possible to use an exernal rectifier and filter capacitor to feed the VFD's DC bus. If the DC bus will take 680V DC you can use the 480V supply directly. Otherwise you need to drop the voltage closer to 418AC / 580DC. Two standard 30V dual secondary 500VA transformers wired in buck will drop you 480V to 420V.

However doing this requires some knowedge of power electronics and motors. The easy / safe solution is Clives number 3 suggestion to change the motor and use a VFD. It will pay for itself in power bill savingscompared to a rotary converter over the years and make the lathe more saleable of you don't keep it.

The same goes for other 3 phase machines. Try to buy one with a low voltage or Star/Delta motor or just change it. Don't forget you can sell the old motor to get some cost back.

I would not consider a rotary converter unless it was free and preferably delivered for free.

Robert G8RPI.

Edited By Robert Atkinson 2 on 17/05/2020 09:48:14

16/05/2020 21:31:16
Posted by Robert Laurenson on 16/05/2020 20:39:06:

Robert G8RPI.

Hi Robert

Thanks for the very detailed response.

That is fully understood, just out of interest, the Unique 3 phase book i mention has a reference to the very supply i have, and as far as i can make out it seems that the basic principle of the transformer is a basic transformer with 2 parts, 1 side being would to 240v, and the opposite side being wound with 3 seperate windings to 440v and the phase angle then corrected on the output with capacitors. I havent bought the book but from the research i have done it seems as though that is the basics of it.

In theory would that work? I mean from looking at his videos and reviews of the system it seems to work but im still not convinced enough to give it a go yet without advice from someone clued up on these type things?

Robert

Hi,

You can get any phase shift with an lnductor and capacitor with a fixed load. This is how the circuit you have seen works. Unfortunatly a machine tool motor is not a fixed load. The transwave and similar "converters" do this with component values for a typical motor and switched capacitor or taps for adjustment. It's not perfect but works. Often an unloaded motor is connected in parallel and turns all the time. It's inductance tends to swamp changes in the load reactance and it's rotating mass acts as an electrical flywheel.
With the current low cost of VFDs I don't see why anyone would bother with this type of converter, just use a single phase in 3 phase out VFD and leave it set to 50 or 60 Hertz if the machine or motor is not suited to variable frequency / speed.

Robert G8RPI.

16/05/2020 19:59:10

This supply scheme is similar to that used in North America for domestic supplies. The NA one is 115V- 0-115V 180 degree phase shift to each house. It is used in some remote areas in the UK. Two wires are taken from the 3 phase high voltage (probably 11kV) supply and run to the remote location. Thi is of course single phase as there are only two wires. For each small group of consumers there is a transformer. In the simplest solution this would have a single 240 V (41.66:1 step down) output winding for the whole load at 240V. However the physics of transformer design means that a pair of windings connected 180 degrees out of phase use less core material. Splititng the load across two windings also means thinner wire can be used making winding easier. This scheme is called "Split-Phase" and uses a single (20.8:1 ratio) winding with a center tap. The center tap is the neutral for both supplies. Normally each consumer would only have a single 240V connetion but heavy users may have two. The voltage between the phases is 480V (if they were 120 degrees apart it would be 415V)
It is not possible to simply generate 3 phase from this type of supply. There may be confusion with two phase 90 degree systems (phase quadrature) which can be changed to and from 3 phase 120 degree using a pair of transformers in a arragement called Scott-T. To run a 3 phase motor you will need a converter either a electromechanical (e.g. transwave) or solid state (VFD) type. In theory you could feed a VFD with both phases via a pair of rectifiers but it's hardly worth it for such a small motor.

Robert G8RPI.

Thread: Identify plastic glue
16/05/2020 15:10:21

if the old sealant peeled off, it clearly wasn'y solvent welded. The two part glues with mixing dispensers are typically epoxy or acrylic. Epoxy is not normally flexible so an acrylic is more likely. A two part silicone i also possible. For something readily available and durable I'd suggest a good quality clear RTV silicone. This may take some time to set fully so not so suited to a production environment hence their use of a two part product which are typically faster setting. At least with RTV you can remove it without damage.

Robert G8RPI.

Thread: Myford ML4 Restoration: Headstock bearings and spindle removal
15/05/2020 19:09:10

I've got to agree with Brian on the pulley / Bull gear locking. The Myford instructions clearly say to unscrew the grubscrew in the pulley. Some ML1/2/34 have had a groove cut in the front headstock bearing casting to give access o the Bull gear locking screw. I wonder it this was to counter a seized pulley.

Robert G8RPI.

15/05/2020 15:21:55
Posted by Jon Cameron on 12/05/2020 10:33:15:

Hi Brian, Luke

Ive found the article by Martin Cleeves. It is indeed for an ML4, my spindle has the earlier spindle and nose thread of 7/8" 9TPI, therefore it only accommodates an MT1 taper and passes 3/8" stock. Below youll see a scan of the article, which also shows a grinder attachment for the rear of the lathe spindle. Something handy if you only have the one motor, though not recommended as the dust and grit would not do your precious lathe much good. Though the rest would be handy for setting up in front of a bench grinder, to assist with grinding HSS, or Carbide tooling. Something that Luke might like to look into for his tool grinding, it is certainly something ill be doing.

Jon,

what a tease! You can't read the dimensions! Any chance of putting a higher resolution scan of the spindle drawing in your album or giving us the magzine issue information?

Robert G8RPI.

Thread: Source of CNC plastic for software proving purposes
14/05/2020 15:07:50

Driving a tool into a block of foam or wax is much less likely to wreck the machine than doing the same into a block of alloy. It's not the cost of making the material, it's what the market (big CNC companies) think it is worth. Even a minor crash that just needs re-alignment can cost thousands of pounds in lost production time. A easy to use test material can be a good investment

Robert G8RPI

Thread: Possible protection from Covid
13/05/2020 17:50:51

I'll just wear my full face twin filter respirator

Thread: Fixing lenses and mirrors into mounts.
13/05/2020 12:47:07

Mirrors and other optics on scientific equipment I've worked on were almost always secured to aluminium alloy mounts in a recess and 3 or 4 small spots of adhesive. Typically this was a filled opaque epoxy probably with thermal expansion between glass and alloy. Some use toughed acrylic like Loctite 330 (sometimes repackaged as optical adhesive with much inflated price tag)

There is excellent guidance here

https://wp.optics.arizona.edu/optomech/wp-content/uploads/sites/53/2016/08/24-Mounting-optical-components-1.pdf

Robert G8RPI.

Thread: Used Lathe Pinnacle PL1340C Gap Bed
12/05/2020 18:20:22

It certainly doesn't look cared for and its not clear what is included in the sale. If there is a 4 jaw chuck and a bunch of tooling that could make a difference. I notice he has put a phone number in one of the images which is against ebay rules because it indicates they ma be trying to sell off ebay to save fees. Trouble is while you might get a better price you loose your protection if you buy off ebay. The seller may not have usesed it much but what about previous owners?
It's a gamble unless you check it out first. Could be neglected but unworn and un-damaged or a complete wreck.

Buyer beware.

Robert G8RPI.

Thread: Box-Shifters and Quality Assurance
12/05/2020 15:09:47

Gee's in Cambridge burnt down in July last year.

Thread: Thermal fuse reliability
12/05/2020 15:02:05

These thermal fuses have a spring contact held closed by solder with a specific melting point. When the solder melts the spring pulls the connection apart breaking the circuit. The solder can suffer from metal fatigue and this causes failure. If the units normal temperature control works with a new fuse then it was just an old age failure of the fuse. If the new fuse trips or unit overheats you have another fault and the thermal fuse was doing it's job.

Robert G8RPI

Thread: questions about setting up my Myford ML4
10/05/2020 20:20:57

Hi,
Have you disengaged the leadscrew nut before trying to use the rack traverse? Does the slike move at all?
I also note the headstock beaings appear to have screwdown greasers fitted. The bearings need oil, not grease. If there is grease in the the lubricators it will need to be stripped and cleaned out.

Robert G8RPI.

Thread: Oscilloscope kits - any recommendations?
10/05/2020 16:25:52
Posted by Bazyle on 10/05/2020 12:10:47:

If not leading the thread off topic too far is there a low frequency spectrum analyser? I'm thinking in terms of analysing lathe vibrations so low frequency like audio range.

The Picoscope software has an FFT function built in so they also act as spectrum analysers. Their automotive software has specialised vibration analysis and balancing functionality and they sell accerometer kits for it. https://www.picoauto.com/products/noise-vibration-and-balancing/nvh-overview
Unfortunatly it only runs on the automotive versions of their 'scope adaptors. As these have 12 bit resolution (most 'scopes are 8 bit) it works quite well. I do have one of their automotive 'scopes and accelerometers but have never need to use it for vibration. If anyone near Cambridge wants to have a play after the lockdown I'm game.

Robert G8RPI.

10/05/2020 12:26:56

Plus 1 for Picoscope. Been a happy customer personally and for work for over twenty years. For beginers 'scopes are a bit like welders, it's easier to get good results with a better model. There are two problems with the low end models, low bandwith (maximum frequency you can measure) and limited input voltage, often only 5V maximum. The latter can be made worse by non-standard input impedance which means standard 10:1 probes can't be used. A 200kHz 5V unit is just about good enough for looking at a caliper based DRO. A mid level range between the low end stuff and Pico Technology is sold by Hantek but I've never used one. If you have space a "proper" conventional oscilloscope could be a good option. Hameg, Philips and Farnell are brands to look at as well as the obvious Tektronix and HP.
Ebay may not be the best place to buy a 'scope. A bit of a "sleeper" is the HP 54600A/B range. These are digital 'scopes with a CRT display. The are more compact than a conventional CRT 'scope because the TV type CRT is much shorter. You can get a 54600B 2 channel 100MHz (2MHz single shot) model from Stuart of Reading for £75 (plus VAT). The 54600 cost over £2000 new in 1993. Stuarts are a well respected dealer. The higher specification 546xx models especially the "MegaZoom" models are even better. The 546xx gets a lot of bad press on the web mostly from Tektronix snobs. My 54645D is my favorite non PC based 'scope even above much more modern and expenive ones at work.The user interface is excellent. For PC use I have 3 Picosopes.

Robert G8RPI.

Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

Latest Forum Posts
Support Our Partners
Warco
Eccentric July 5 2018
emcomachinetools
ChesterUK
cowells
EngineDIY
Eccentric Engineering
Subscription Offer

Latest "For Sale" Ads
Latest "Wanted" Ads
Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues

Social Media online

'Like' us on Facebook
Follow us on Facebook

Follow us on Twitter
 Twitter Logo

Pin us on Pinterest