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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: rivet snaps
25/06/2022 16:47:48

Oh!

Thanks.

JA

25/06/2022 16:24:31

Just resurrecting a recent topic.

I am about to do quite a bit of riveting and, being lazy, will buy some rivet snaps. I assume the dimension quoted for the snap size is the diameter of the formed rivet head and not the shank diameter of the rivet. Am I correct?

JA

Thread: Free Fusion360 subs ended
25/06/2022 15:43:22

To me the question is "What happens after three years?"

I think John is using a paid for version and not the free option. I am aware you gain quite a bit more if you pay.

Up grading my PC would bring advantages. I am told that SSDs give far better performance. However I ask myself "Can I face the hassle?" At present, it is no. I don't really need solid modelling.

JA

25/06/2022 11:43:48

I have used Fusion360 for about 15 months and will probably give up with it. It is now very slow and bringing items back from store, "the cloud", can take a very long time.

I read the website that Gary mentions as the free version can be used for three years with yearly renewal (which was easy). After that you have to pay to access your work. I may have misunderstood the website and got this wrong.

JA

Thread: Edge finder lubrication
20/06/2022 17:06:17
Posted by SillyOldDuffer on 20/06/2022 16:05:41:

All I can confirm is that my edge-finder has better repeat performance than my milling machine's DRO and mechanical dials, neither of which are top-end. Off hand I can't think of a way of measuring the accuracy of any of my location tools. I'm stuck!

sad

Dave

Dave

I think this is crux of the discussion. Most of us use tools that are just (about) adequate. Once comparisons start being made we, model engineers, are only just above where our predecessors were 200 years. After all nations have spent lots of money trying to improve measurements.

JA

20/06/2022 14:46:25
Posted by Tony Pratt 1 on 20/06/2022 13:40:54:

In another recent thread I posted this:

One of my books gives figures for some locating methods, unfortunately not all of them.

From worst to best:

Cone into hole (how I do my rotary table) - ±0.005"
Wiggler needle - ±0.003"
Laser pointer - ±0.002"
Electronic Edge Finder - ±0.0005"
Mechanical Edge Finder - ±0.0002"

Interesting how good a mechanical edge finder is, ten times more accurate than a laser pointer! But laser pointers are designed to find cross-hair markings or centre-punch holes, which an edge finder can't do, and a laser pointer is quicker and more accurate than a wiggler needle, which I also depend on.

Note how difficult location inaccuracies make it to work accurately in tenths!

Dave

I personally doubt a mechanical edge finder will repeat to .0002", in my book the most accurate method is to 'split the edge' with a DTI, & in reality .001" or under positional tolerance is jig boring territory.

Tony

Edited By Tony Pratt 1 on 20/06/2022 13:44:35

Edited By Tony Pratt 1 on 20/06/2022 13:53:16

I fear that this posting is being hijacked.

My feelings on the above table are:

  1. Cone in hole is better than stated but it does depend on feel.
  2. Laser pointer does not approach the stated value because of the diameter of the laser spot.
  3. Mechanical edge finder is nothing like that quoted.

As stated I have not knowledge of electrical edge finders.

I would like to know about electronic touch probes, such as those made by Renishaw, which do not rely on the electrical contact between probe and work piece. I know they are very expensive and probably have figures far better than those above. I have no idea if any are sold by model engineering suppliers.

JA

Edited By JA on 20/06/2022 14:47:52

20/06/2022 12:50:15

I now use a simple edge finder without any lubrication. However I am aware that it is not as accurate as a small length of silver steel bar and fag paper, previously used. Since I do not smoke (anything) ordinary printer paper was used as a substitute. It was always 0.004" thick.

I wonder how accurate a simple electrical edge finder is. It must be affected by oil etc hindering the conduction of the current.

One trades accuracy for speed which is never wise.

JA

Thread: Thoriated tungsten electrodes
18/06/2022 15:06:18

In the early 1960 Mercury got into the food chain very seriously in Japan. It, no longer as a pure element, ended up in Dolphins (at the top of the food chain), a highly prized food. A large number of human consumers of Dolphin meat got very badly poisoned

I remember in about 1973 Mercury started to be taken very seriously. I worked as a very junior member of staff in the mechanical engineering labs at Hatfield Polytechnique. In the fluids dynamics labs we recovered a considerable amount from under the floor boards. It came from broken manometers. Also it was common practice to label each tube on a manometer bank with masking tape. Eventually the labels had to be removed so out came the bottle of Xylene.

Thinking back to sixth form at school, it as common practice to dip an old penny in Aquaregia, wash off the acid and then put it in mercury. The result was a nice shiny silver penny which you tried to use as a half crown. Having no success it remained in ones pocket and, after few days, was an ordinary shiny penny. So what happened to the Mercury (not a question).

JA

Thread: FORUM DOWNTIME AND RESULTING ISSUES REPORTING
09/06/2022 17:25:16

Login immediate (up to date version of Firefox and Windows 10).

It strikes me the changes have been relatively painless.

JA

Thread: Thoriated tungsten electrodes
06/06/2022 09:01:53

Thorium is radioactive. It emits low energy alpha (I think, from memory) particles that cannot penetrate the skin. However if the dust, from grinding etc, is breathed in then you have problems.

Magnesium alloyed with some Thorium was used in the aircraft industry. It produced a strong light alloy but was abandoned in the 1990's because of environmental problems during casting (what happened to the Thorium Oxide dust when the metal caught fire). The major Magnesium foundry in the UK was in south east London.

JA

The foundry had an open casting floor and if a fire had taken place with Magnesium/Thorium alloy  I believe all air conditioning units, where dust could gather, within a 5 mile radius would have had to be turned off and cleaned.

 

Edited By JA on 06/06/2022 09:09:05

Thread: My Faith in Human Kindness is Reinforced
02/06/2022 11:59:14

My experience of humanity is that people are far more likely to help you, give you assistance, for no reward than to rip you off or take advantage of you.

I could give many personal examples but won't.

JA

Thread: Hello - Uni or apprenticeship
26/05/2022 16:47:35

Christine

Really, the world is you oyster.

If you are good at your job the route you take now will make little difference in twenty years time. The major differences are that an apprenticeship will give you some hands on experience while university may not and that university will cost you money. If you are any good a good employer would usually send you to university. A number of my collegues who had done ordinary apprenticeships were sent to university, in some cases straight onto post graduate degrees.

I think I would have interviews with a few major engineering companies and see what they say and offer.

Unless you become highly specialised you should end up with transferable skills and knowledge.

All the best for the future

JA

Just seen Frances's last posting.

An internship allows you to have a look and get noticed. Most companies will pay you during the internship. My niece was paid the average national wage by RR during her summer vacation from university ten years ago. We even had a person in the office for six months on a pre-university internship. I should say she was not in the way and made a useful contribution.

Edited By JA on 26/05/2022 16:54:09

Edited By JA on 26/05/2022 16:55:37

Thread: A question about reamers and hole tolerances.
17/05/2022 19:46:32

MichaelG

Thanks.

I have downloaded the document which should be useful, not that I will be reaming copper.

JA

17/05/2022 17:30:36
Posted by Tony Pratt 1 on 17/05/2022 17:25:00:
Posted by JA on 17/05/2022 16:58:58:

I think the above table is a load of rubbish. It is interesting that copper is included. At work we broke over 60 1/2" reamers trying to ream holes in a copper block. We gave up and the research project was abandoned.

Are you having a laugh? Copper is definitely a material which can be reamed if you know what you are doing.wink

Tony

We spent thousands of pounds of your, the tax payer's, money on that project.

I note that your profile says nothing about your experience.

JA

17/05/2022 16:58:58

I think the above table is a load of rubbish. It is interesting that copper is included. At work we broke over 60 1/2" reamers trying to ream holes in a copper block. We gave up and the research project was abandoned.

This is the table I use:

tolerances.jpg

and the associated fits are:

fits and limits.jpg

A large D does not appear in either table. Given that reamers are usually H7 you can decide on the shaft diameter.

For completeness I include a third chart:

machining processes.jpg

I do try to work to the above tables.

JA

Looking again at Robin's chart I think the "D" in the right hand column is a typo.

Edited By JA on 17/05/2022 17:02:37

16/05/2022 09:13:28

I have never used Amazon for anything other than books and, for what it is worth, no longer use the model engineering suppliers for reamers, milling cutters etc.

The industrial suppliers are quite happy to take your money, are no more expensive and usually give a next day service. I can recommend, just as a satisfied customer, Drill Service (Horley) Ltd.

JA

Thread: .dwg and .dxf files
12/05/2022 12:49:42

Many thanks for the above replies.

I have spent the last few hours drawing the part in TurboCAD and have just sent off both the .dwg and the .dxf files. I took Andrew's advice and produced a complete drawing.

Now for the replies from the cutters.

JA

11/05/2022 20:31:24

I have contacted some waterjet cutting firms for getting some plates cut. I included a .pdf file of what I want (the only way you can get a drawing out of free FUSION360). They are asking for either a .dwg or a .dxf file.

I can produce either of these using TURBOCADS. Before I produce a file what should it contain: Just the outline of what I want? Plus dimension? A complete drawing with a border and text box?

JA

Thread: Code of Conduct
11/05/2022 11:30:56

In the early 1960s, just after Lady Chatterly's Lover, lots of people were so prim and proper that they ceased using the word tart in cake shops etc. Keeler was used instead.

Are these simple Anglo-Saxon words really that offensive? However I expect the use of the terminology male and female for screws and nuts is frowned upon in this forum.

JA

Edited By JA on 11/05/2022 11:34:30

Thread: Gallium
08/05/2022 16:46:49
Posted by Michael Gilligan on 08/05/2022 14:09:14:

Would I be right in assuming that only a few of the contributors to this thread have yet read the paper that was linked in the article ?

MichaelG.

.

Yes, in my case.

I had a very quick look at the article and then got on with life.

JA

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