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Member postings for JA

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

Thread: edm machines
07/04/2019 17:56:34

As requested, 3 photographs of the electronics box. The names of the controls are not stickers but an annotated photograph as a reminder to me (dither is the period of withdrawal of the electrode to allow escape of the debris).

annotated.jpg

dscn7482a.jpg

dscn7484a.jpg

Ben suggested using an old PC box. I had one but found its construction so complex that it became easier to build my own. The box is possibly too small but the use of 12" long metal stock allowed a quick and easy construction.

The circuitry is not complex. The power is provided by 80vAC through a full bridge rectifier. The maximum power is 650VA and is controlled by a bank of forced air cooled resistors. The switching of the power is by a MOSFET controlled by a 555 timer. Another 555 timer is used for the dither period. The electrode position is determined by comparing the discharge voltage with a required operating voltage and a minimum voltage required to prevent the electrode hitting the work. The electrode position is driven by a simple servo motor. I know there are other ways of controlling the discharge and position of the electrode but as an electronics simpleton I am happy with most of Ben's circuitry.

I have to say that the project is very much "work in progress". I have just started on the electrode head.

07/04/2019 09:51:05

I am building Ben Fleming's second EDM machine. It is described in his book "Build a Pulse EDM machine". The book is not cheap and the electronics is even more expensive. I choose the pulse design because sensible capacitors for the resistor-capacitor set up used in his first book are hard to find.

Ben's second machine uses a voltage of around 100vdc which is switched by a MOSFET (a bank of 6 in his case) at frequencies up to about 20kHz. There is also provision to lift the electrode every ten or so seconds to flush out the debris. Everything is adjustable in the design, the front panel of the electronics box is very intimidating.

I can provide photographs etc if anyone is interested.

Thread: Furnace Silver Soldering
01/04/2019 19:34:34

Has anyone tried furnace silver soldering on a model engineering scale? I would like to know if it is feasible and, if so, what are the pit-falls.

I see it as a good alternative to the conventional propane torch technique. It seems to offer advantages when soldering a complex assembly with step soldering where accurate control of temperature is required. Obviously the equipment cost is higher but pottery kilns are readily available and can easily reach silver soldering temperatures. However the furnace/kiln would need an inert gas purge system.

In industry furnace silver soldering is the preferred technique. A major reason is that with an inert atmosphere very little or no flux is required thus reducing cleaning time and costs.

I have done a very quick look at the internet and have found a very good introduction to furnace brazing by Air Products. It is obviously aimed at industry.

Thread: Making split bronze bearings [ silver soldering ]
22/03/2019 12:31:32

My attempts at using solder and glues failed so I made a proper fixture to hold the halves. This allowed the ends to be faced in addition to the boring of the bearing.

A little bit of thought and accurate machining is required.

bearing fixture 2.jpg

bearing fixture 1.jpgJA

Thread: Silver soldering a blind 'mortise and tenon' joint.
20/03/2019 23:31:11

My comment is a bit late but here goes.

A couple of years ago I tried a "tinned" silver soldered joint to see if it worked. It was successful and good. But for the life of me I have not idea why one would ever use such a technique!

JA

Thread: Blackening steel parts
30/11/2018 20:02:26

I posted this question a few years ago.

I was unsuccessful in finding a company that would hot black mild steel (using caustic soda) so I did some trials. I found that I could successfully black screws and nuts down to 12BA by the blacksmith method.

I did over 200 items smaller than 4BA without a scrapper: Heat each item, held by steel wire, individually to red heat in a flame of a cooker gas ring and drop into clean 32 hydraulic oil. Simple but boring.

Since then I have found a firm in east Bristol that will hot black mild steel.

JA

Thread: Chucks
22/05/2017 13:26:18

During my period in the apprentice training school I never saw a three jaw chuck. We were taught to centre a round bar in a four chuck using a piece of chalk (possibly because we could not be trusted with a "clock", possibly because we would get totally confused).

The three jaw chuck I have at present is so bad it cannot be used for anything (this is being corrected).

Therefore: Four jaw chuck, collets followed far behind by faceplate and turning between centres.

JA

Thread: What Did You Do Today (2017)
19/05/2017 23:48:14
Posted by Andrew Johnston on 19/05/2017 21:24:00:

To make matters worse I've had a rotten day in the EMC lab looking at conducted emissions, ESD and surge. The technician didn't seem to know what he was doing. Having been told there's a new standard coming out regarding conducted emissions from signal lines he promptly connected the CDN up back to front. And while we we're twiddling our thumbs waiting for the AC surge tests to complete he bored the pants off me with talk about websites and apps that allowed him to get free texts and SMS on the mobile dog 'n' bone. It's all very clever but I really don't need an app to remotely tell me if the garage door is open if it starts to rain.

Andrew

I am sorry to ask this, but do you really need the money?

If so, there must be better options.

JA

Edited By JA on 19/05/2017 23:49:32

Thread: Any Bristolians out there!!!
15/05/2017 16:57:34

Thanks for the impressions, Geoff.

Real Bristolian is not really West Country. It involves the use of infamous Bristol L which is put on the end of any word ending in a hard vowel. Idea becomes ideal, area areal and so on. The clever Bristolians can even put it in the middle of words. Unfortunately its use is disappearing.

JA

Thread: Which coolant
14/05/2017 17:27:03

I use Morris's CORA B neat cutting oil for all metals except brass and cast iron which are machined dry. I machined aluminium bronze recently with and without cutting oil, it made on difference.

I think there is already a thread on this subject.

JA

Thread: Home-made Screw Tap - Advice Please
12/05/2017 18:03:10

Dave

You are having fun.

I think making a tap would be difficult without specialist tooling. Even for a tap for brass I would start with silver steel. First do the machining, then harden and temper and finally sharpen by grinding the cutting faces. Easy, no, but this is a training exercise. And don't use cutting paste with brass.

I would thought a better exercise would be to screw cut an internal thread. It would be easier if the diameter was larger and the thread pitch finer. You should make male gauge first. I will not give any further advise other than think a lot about the job.

All the best and I will enjoy reading the replies.

JA

 

 

Edited By JA on 12/05/2017 18:07:02

Thread: Screwcutting Crashes -
11/05/2017 11:47:04

Dave

Is this a first attempt or is for a specific job?

If it is the first, it would be far better to start with a something like a 1/2" mild steel bar. Put it in the chuck, face and centre drill the end. Then turn down the bar to the core thread diameter for a short distance. Next Release the bar and move it about to give about six inches of length, reclamp the chuck. Support the free end with a centre in the tailstock. Using a parting off tool at low speed cut a groove to the same diameter as the thread core close to the chuck.

Now everything is of a sensible size and you will have a run-out at either end of the thread for the tool.

Quick comment after reading Duncan's reply. If numbers are involved write them down on a piece of paper first.

JA

Edited By JA on 11/05/2017 11:49:36

Thread: Any Bristolians out there!!!
10/05/2017 23:07:37

Geoff

Please give us, or at least me, your impressions of the fine city of Bristol.

JA

Thread: Screwcutting Crashes -
10/05/2017 23:03:08

Dave

The only reason for going to the bottom of the class is that you failed to check the clearance between the chuck and everything else through the whole machining operation before starting the lathe.

I do not know the lathe you are using but you need more space. As far as I can see from the photograph there are two ways of doing this:

  1. Increase the overhang of the tool. One is advised to keep the overhang small but the cuts during thread cutting are light and any roughness can be removed by using a die as a thread chaser.
  2. Move the work further away from the chuck. This will probably necessitate the use of a centre in the tailstock which may give you a few difficulties.

I have frequently cut threads, externally and internally, and always quite a bit of thought is required in setting up the job. As you have done I have always angle the top slide.

I feel that the successful cutting of an external thread is the second right of passage with a lathe (the first being setting up a round bar in an independent four jaw chuck).

You won't be bottom of the class for long.

JA

Thread: Any Bristolians out there!!!
10/05/2017 19:53:36
Posted by Mike Poole on 10/05/2017 19:40:52:

I think it was the Luftwaffe that messed it up but I don't think the architects did much of a job on the rebuild. I have visited a number of German cities where they have done a superb restoration from piles of rubble.

Mike

As in Birmingham the Luftwaffe just helped the planners to achieve their aims. I agree with you about some German cities and towns such as Celle.

JA

10/05/2017 19:09:54

In addition to the above suggestions: Clifton Village, because it is relaxed; The Underfall Yard, a boat building yard and museum next to the Nova Scotia (I have fond memories of the Scotia from years ago); Broadmead shopping centre if you want to see how the planners of the 1940s & 50s can mess up a city.

The two bridges over the Severn are a bit difficult to get to by public transport. The new bridge is best seen from Severn Beach which is at the end of a suburban rail line from Temple Meads. The journey will show you a side of Bristol that the tourists never see and there is nothing at Severn Beach other than the bridge. The old bridge can be crossed using the Chepstow bus. Getting to the actual bridge is another matter.

Unfortunately the new aircraft museum on the north side of Filton airfield is not opening until later this year.

Bristol is a great vibrant city. The traffic is a bit dire but the city buses are pretty good and most of the city is walkable. Unlike Bath it is not a tourist trap.

JA

 

Edited By JA on 10/05/2017 19:11:36

Thread: Maneton clamps
10/05/2017 11:21:02

I feel it is only fair to make accessible to all of what I sent to Windy. Therefore I will be putting the information in my photo albums under Mineton Clamp over the next few days.

The photographs are of an exhibition piece showing the rotation training of a Bristol Centaurus engine. The drawings are assembling drawings for a Bristol Hercules crankshaft and the article is from "Aircraft Production" magazine of 1944.

JA

09/05/2017 19:50:36

Windy

I have sent you a PM.

dscn6493.jpg

JA

Thread: Setting up shop
07/05/2017 23:12:16

The lead screw cover was a thin sheet of aluminium. It seemed like a good idea and on such a lathe cannot do any harm. On an M7 or S7 Myford it would have to be cut back if a gearbox was fitted.

JA

Thread: The diesel controversy
07/05/2017 23:06:13
Posted by Mike Poole on 07/05/2017 22:30:50:

Speedway and grass track bikes run on methanol and I think some classes of drag racer do. Fuel consumption is massive and the engines run very cool. The joke about jetting an Amal for speedway was just put a 1/8th drill through the main jet. Fires are nasty as they are not visible.

Mike

The 1.5 litre supercharged Alfa Romeo Grand Prix cars of about 1951 ran on methanol and had a fuel consumption of 0.75mpg. Mind you the engine had a large valve overlap that allowed the blown through methanol to contribute significantly to the cooling.

I remember seeing a Triumph 500cc twin bike at a hill climb in the very early 80s with no finning at all. It was a methanol burner and it would not start properly. It was just too cold but when it did go it was very quick.

JA

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