Member postings for Martin Dowing

There are oversupplied *cities* in China, which no one want to inhabit and which are going to be thrown away and you are fretting about bikes.

Their carbide inserts gone even cheaper and now I am getting these for $0.30 each... and they are working very well.

Martin

I do import many things from UK, I have family there and also friends in academia and industry, spent most of my life there etc.

However items like bar stock is best to source out locally where you are. Sending small quantities will treble your bill.

Your ideas about suitable grades of aluminium are helpful but barstock of required diameter and of such grade is difficult to get here and for some reason soft grades of aluminum are commonly sold and these are of no use.

Martin

I am currently living in Poland and they have what I described.

Occassionally, with much pain you can get 6xxx or even 7xxx but usually something very soft and useless is on offer.

Martin

You need to insulate microwave walls and door with light heat insulating material which is used also for thermal insulation of fireplace. this material is cheap and very easily formed.

Alternatively you can purchase similar looking material used in furnaces.

Both are wonderful heat insulators.

You *must* ensure that your product is microwave transparent, eg it does *not* get hot when stuffed up to microwave. After few minutes it may get a little bit warm but nothing more than that. In any case avoid running microwave on no load for more than 2-3 minutes or you may damage magnetron and other circuitry.

To join pieces of insulating material you may use an adequate fire resistant cement. Cement also must be (when dry) microwave transparent, test it as your insulating material. Appropriate cement is alumina based and certainly *not* zirconia based as the latter will absorb microwaves and get very hot and it is not what we want.

Make sure that thermal bridges are absent, eg that thermally insulating layer is protecting entire interior and door. 25mm of meticulously fitted insulation from all sides will do if you are not aiming above copper or gold (1100*C) and do not intend to run extended sessions, few hours long. Otherwise apply 50 mm thick insulation.

You must provide for pressure equilibiation measures.

Now you need a crucible and this should *not* be microwave transparrent. The best (and cheap enough) are *carborundum* (silicon carbide) crucibles and preferable variety is one nitride bound but others are also good.

Another and more expensive option are those made of zirconia.

You will recognize suitable crucible by observation that it gets very hot once stuffed to microwave. If left too long it will get red hot and damage not thermally insulated microwave. Fire and property damage might result.

To reduce risk of fire it is also of paramount importance to use new or exceedingly well cleaned up microwave.

Now fill scrap metal to your crucible and stuff it to microwave. My initial trials were done in block of mentioned insulating material and silicon carbide crucible. Microwave is not lined up with insulation like described but a block of insulating material encasing crucible from all sides is good enough for prove of concept experiment.

20 grams of scrap silver was smelted within 20 minutes in 800 W microwave. Beauty of this setup is that most of microwave energy is going only into crucible and its load.

If you want to use microwave as a muffle, stuff few lose silicon carbide heating elements in. You will get hot chamber this way.

There is much more to it, above are explained only basics sufficient to get one going.

I may write something about it in the future, once some basic work to develop this tech is done. For example flimsy plastic parts in door will need replacing with something sounder, inlet and outlet of inert gas is to be installed etc. Interlocks switching off power upon opening of door should be kept and after any modifications of the oven one must ensure that microwaves do not leak out etc.

Some basic setups working with household microwave sufficient to melt a sample of glass are sold on Amazon. Search for "microwave kiln".

I am developing substantially better product than this.

Martin

Adding 2% of copper is not a great expenditure, yet for some reason 1050 prevails.

Martin

This 1050 grade is widely available and at least in my opinion it is good for nothing.

I do not have any difficuty in machining it but parts made of it do not last long, so they are best if not made at all.

I love 7xxxx grades as some of these are very good but it is not easy to get them. Silumins are OK but until I have adapted my old microwave for smelting them, they are not usable for me.

NB. converting microwave into smelter is an interesting project of its own and not costly either. I can already smelt 10-20 grams samples of silver there but some more permanent thermal insulation of walls and door is needed for more sensible quantities. Bonus is that it could allow for smelting under argon to produce quality melts if necessary or should be usable for brazing in inert gas, eg there won't be scaling, I hope.

Martin

Yes but basically 3 versions are available.

1. Glass fibre reinforced - More suitable for NASA but also used in printed circuit boards working in high temperature (grades resistant up to 250*C are available).

2. Cotton cloth reinforced - suitable up to 120*C used in general engineering like gears etc.

3. Paper reinforced - marginally weaker than 2. but still excellent.

Resins do vary but they are generally phenol - formaldehyde polycondensates of comparable properties. Sometimes melamine-formaldehyde polycondensates are used but such products should not be called "Tufnol" or "Textolite" and are yellow or whitish rather than brown.

Resins are engineered rather for chemical and thermal resistance.

When heated characteristic smell of phenol and/or formaldehyde can be felt.

Martin

It will be 2 step pulley working with 10 or 13 mm belt, so the plate would need to be more than an inch thick.

Martin

Hi,

Thanks for comments, all of you.

My Tufnol is "cloth type" and it gives away lots of dust while turning. It turns brilliantly apart from the dust and it seems to be hard, certainly better than crap (eg easy available) grades of aluminium.

NB. I do not understand why commonly sold grades of aluminum bar are basicaly good for nothing apart from generating hydrogen via reaction with solution of caustic soda if at very little or no additional expense a reasonable material could be made.

So base on what you say it seems reasonable to produce larger bore and install keyed & flanged brass/bronze/steel bush press fitted in presence of retainer (Loctite?). I will proceed that way.

Martin

It will work with 10 or 13 mm V-belt at effective diameter of 6" and maximum speed 1450 rpm. Single belt, expected to transmit 1/2-3/4 horses.

Martin

I need low inertia pulley, eg ones made of low density material.

I was searching various grades of aluminium but required bar sizes are available ex stock only in soft grades which wear easily. I am not equipped well to cast one myslef albeit this will change - conversion of microwave into nonferrous metal smelter is under way and initial tests are promissing (sample of silver was smelted).

Meantime I have Tufnol block of adequate size to produce what I need.

What do you think about Tufnol as material for a pulley? It must have good tribological properties if gears are made of it (including gears of tumbler reverse on my ML7).

My concerns are about coupling Tufnol to steel shaft. Keyway in tufnol might get damaged by steel key. Should I make a Tufnol key as well or is it better to bore bigger hole in the center and fit (glue permanently) metal ring with a bore to adapt shaft?

Martin

Buy CBN insert (Chinese ones are cheap enough and if you are not tight on money look on Sumitomo Electric range) and no imaginable steel will be too hard to work with. Toolholders are the same like those for standard carbide inserts.

Claims that these need extremely rigid machine to work with are rather mythology - my ML7 copes well.

Try to keep surface speed above 1.5 m/s or so. Avoid turning *soft* steel with these inserts - they hate it and will get damaged easily.

You will also get a beautiful surface finish as a bonus.

Martin

I have made these 2 bushes out of tufnol.

Paid attention to get good accuracy which hopefully will help to get wheel centered better to reduce dressing efforts and possible vibrations in use.

They are a bit tight on spindle, though easy enough to locate while pushing and twisting but the wheel feels like h6/H7 fit - I know it is not but just feels like - easy slide and no play.

Another thing I have found that I can fit 25mm wide SiC wheels on nominally 20mm wheel grinder.

Wheel catching plates have 3.5 mm recess and I believe that 1 mm deep recess on each plate made of sound material of the same thickness is more than enough. So I can win 5mm!

It is also worth to notice that 25 mm wide SiC (silicon carbide) wheel has a weight approximately the same like 20 mm wide corundum wheel because of lower density of silicon carbide (3.2g*cm-3 v. 4g*cm-3 for corundum).

Hence machine will work with a weight (and angular momentum) which it was designed for.

@Duncan Webster

If you poured lead - bismuth alloy of appropriate composition, you would not face contraction upon solidyfication issue.

Martin

NB. I like Tufnol - it is synthetic polymeric material which I can trust. Resistant to oil and  temperatures in range of 100-250*C, depending on grade. Good insulator.  Mechanically sound and easy to work with.

Edited By Martin Dowing on 24/03/2018 21:51:34

Edited By Martin Dowing on 24/03/2018 22:08:04

1. Most likely taper in your spindle is not made correctly - will need reboring. This is to address horrible runout of dead center. If it is really 3mm spindle may actually need *remaking*.

2. Bearings will need replacement and/or rescraping. Installation of chuck increases runout - worn out bearings.

Bent spindles are very rare and 3mm runout on dead center in the spindle taper combined with relatively slight runout on spindle nose suggests something else.

Martin

Titanium TiAl6V4 cuts very well with usual tooling as long as these are sharp.

Surface finish is like a ground one, with satine touch on it. It is far easier to get beautiful finish on titanium than on carbon steel BDMS type. Threads made of titanium are working smoothly, and their surface is a spotless one.

Due to rather poor thermal conductivity deep cuts are not advisable if good cooling is not available. Overheated turnings can catch fire.

Turnings can be burned, they produce brilliant white light. My wife is a customer for these. Whenever I turn titanium, she will collect all of them, make some kind of bundle, set it alight and observe how white flame is travelling along wires.

Martin

@David,

Supplier of the wheel have already advised me that "Noone is asking for these and we don't have them. Make your own or go to someone who has a lathe so he will make it for you".

Wheel is from Andre Abrasives, so it is a reasonably good one.

@Tractor Man,

Just want to make sure that wheel will run true and not develope a "throw" which leads to vibrations etc.

Btw, I have a "bloaters are also labels" case - thick paper

Martin

Edited By Martin Dowing on 23/03/2018 20:06:09

I am intending to replace grinding wheel on offhand grinder.

Want to install a green silicon carbide one and I need to fabricate adaptor ring because spindle is 5/8" and wheel has 32mm hole.

Wheel is 20 mm wide, very much like one already on machine.

I want to make a ring out of textolite (tufnol) bar (which is at hand). It is going to be 19.5 mm wide, eg 0.5 mm narrower than a wheel.

I want to make it rather close fit but avoid situation were forcing it in is necessary, particularly into a wheel hole.

Is that OK or I need to look on something else as well.

Martin

Many thanks for comments and opinions.

Seems that best approach is to use perhaps cast iron gibs as Howardt suggests and if for whatever reason this cannot be done some gauge plate steel will do, particularly if slide is rarely used.

Martin

Which material is best for gib strips of slides?

Martin

@ CuP Alloys 1,

Mamy thanks for your comment, this is very valuable.

So you was working on extrusion ratio ~70. I bet, you had to heat this Cu/P wire quite considerably before extrusion as it is quite brittle at RT. I would not suspect that such an extrusion ratio is possible on 30 ton press, unless extruded metal is rather soft. Probably extrusion itself was heating your billet even more.

What was used for lubrication? how piston was removed after job was done? By pushing up die from the other end?

For my trials I intend to make carbide die by brazing broken small inserts into a robust ring which will be placed on the botton of bore. Initially they will be ground to approximately circilar shape. Smaller ones have a hole about 2.8mm and nice wire should be produced.

It is sad to hear about your business troubles from the past. Anything what doesn't kill us will make us stronger but this type of experience is best avoided. Run business myself. Renting rooms for holidaymakers and few other activities.

In the past was working in chemical industry but have resigned.

Martin