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Member postings for Michael Cox 1

Here is a list of all the postings Michael Cox 1 has made in our forums. Click on a thread name to jump to the thread.

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Thread: Internal swing up toolholder
14/07/2011 16:37:45
I have developed a prototype swing up toolholder for internal threading. More details can be found here:
I hope this is of interest.
Mike
Thread: Spark erosion machines .
07/07/2011 12:18:45
Hi Clive,
Today I made a small experiment to try to sustain a spark without the solenoid action. I took the weight off of the rod for the test. I couldget not sustained arc or vibration, not even momentarily, with this method.
I too have noted the effect of finger pressure on the sparking. This was the main reason for adding the weight. The weight certainly increases the total current flow, frequency and erosion rate. If the armature is well outside the solenoid then welding is likely to occur and the force from the solenoid is insuffient to break the weld. However, with the armature well inside the coil then the force is large enough to break the weld and continuous operation is possible.
I was surprised when I added the weight that the frequency of operation went up since additional weight should reduce the natual frequency of oscillation of the spindle. However, your theory about spark shock oscillation may explain this. If this is the case then the main function of the solenoid is simply to act as a weld breaker. This would also explain the fact that the spindle can be oscillating at a steady high frequency of say 50 hertz with very little amplitude of oscillation but occasionally it will make a much larger oscilation and then revert back to its previous steady low amplitude mode. This occasional blip must be when a weld forms.
Mike
 
07/07/2011 08:55:40
Hi Clive,
I hope the latest link to my Mk3 spark eroder now works for you. It works when I test it.
Your post is most interesting and it raises many new questions for me. The operation of the unit is complex and there are so many variables involved.
To get the unit operating at good efficiency seems to depend on the following:
1. Maximise the frequency. Low frequencies mean that the spindle spends very litttle time near the workpiece and therefore much timeis not being used effectively.
2. Minimise the "short" time when the electrode is actually in contact with the workpiece. During the "short" time no erosion is occuring.
3. Maximise the charge on the capacitor. Even at the highest frequencies that I have achieved the capacitor is always charge to near its maximum capacity as shown by my oscilloscope. This is true at almost any setting of my electrode voltage detector. This indicates that the electrode always spends sufficient time away from the workpiece to fully charge the capacitor.
Your ideas regarding spark shock induced oscillation are interesting. If this is true it should be possible to get continuous oscillation even without the use of the solenoid. I shall investigate this further.
Kind regards
Mike
06/07/2011 23:30:54
Hi Dias,
Sorry for the inconvenience but I missed out a hyphen in the link. Try this:
Mike
06/07/2011 21:05:34
The link should be
Mike
06/07/2011 21:03:15
Hi Clive,
I have made some more modifications to my spark eroder and have fitted a motor drive to maintain a constant stroke on the oscillating spindle. My machine also operates at high frequency (circa 50 Hz) and the stroke of the spindle is very small, it quivers rather than reciprocates. Further details are available here:
http:mikesworkshop.weebly.com/a-spark-erosion-apparatus-mk3.html
Mike
Thread: Case Hardening - can't even harden a washer !
30/06/2011 19:11:01
Hi CW,
I always buy metal from m-machine (www.m-machine-metals.co.uk). Very helpful people and can sometimes get special grades on request.
Steel washer are probanly stamped from a cheap grade of steel like EN3. This should be case hardenable. Steel from the local forge is likely to be cheap EN3 also.
Mike
28/06/2011 11:16:08
Hi CW,
 
Like you I have a container of case hardening compound that does not stick to the surface when you dunk the hot piece into it.
 
I believe there are two types of case hardening compounds on the market. One type, Kasenite and its clones, is based on alkali metal ferrocyanides. These melt and stick to the surface of the hot metal and carbon from the ferrocyanide diffuses into the hot surface. Once the powder has stuck to the surface it can be further heated with a torch to maintain a high temperature.
 
The other type, that you and I have, is simply powdered charcoal with perhaps an acivator (barium carbonate?). Like you I have had little success using this product to case harden small parts by the heat, dunk in powder. repeat a few times and then finally quench. Partly I think this is because with small parts like washers there is so little retained heat in the component when you dip it in the powder and it cools rapidly in contact with the powder. There is thus little time for the carbon to diffuse into the surface whilst the component is hot. Maybe it would work better for large components where there is much more retained heat and they would not cool so quickly. All the components that I have tried to case harden have been small so I don't know whether this is true.
 
I have used the compound by sealing the components and powder in a copper tube with pinched of ends and then heating in a furnace to bright red heat. This works well and the components after quenching are very hard. Having said that I can get the same result using just powdered wood charcoal mixed with a little sodium bicarbonate (ratio about 20 parts charcoal to 1 part sodium bicarbonate) as activater, by this process. These ingredients cost very little.
 
Kasenite seems to be in very short supply and none of the usual model engineeering supplies stockists (eg Chronos, RDG etc.) list the product. Maybe it is available from specialist suppliers like gunsmiths. This may be because it is thought to be poisonous. Whilst cyanides are very toxic ferrocyanides are relatively benign. Potassium ferrocyanide is frequently add at a low level (circa 1%) to table salt as an anticaking agent.
 
I hope this information helps
 
Mike
Thread: flip up toolholder
19/06/2011 19:01:18
Hi Pailo,
You don't have to set the top-slide over for any threading operation. Setting it over gives lower cutting forces and sometimes a better thread quality. For small threads (up to 1 mm pitch) in free-cutting materials such as brass or EN1A freecutting steel I usually do not bother the set the cross slide over. For bigger threads and or tougher materials then I set the top-slide over at half the thread angle. Either way works well on a swing up toolholder.
Mike
Thread: Tachometer.
13/06/2011 14:11:34
Posted by Sid Herbage on 12/06/2011 22:36:16:
I haven't read the article but there are potential cheap alternatives (that read RPM) on eBay such as:Cheep eBay Bicycle Computer
This looks to be a possible alternative to the AS11G that I used. However, it is not possible to know what rpm range it would cover without buying one.
Mike
12/06/2011 19:41:01
Hi Ray,
One other point. Despite what it says in the instructions the AS11G works accurately (checked against hand held reflective sensor tachometer) up to well over 2000rpm.
Mike
12/06/2011 19:24:29
Hi Ray,
The AS 11G cycle computer is stocked by the DIY/Home/Garden chain Wilkinsons. They were in stock at my local branch (Widnes) last week.
Mike
Thread: Internal threading on Alu tube problem.
04/05/2011 08:34:58
test post
Thread: Spark erosion machines .
06/04/2011 10:34:12
I have added a page to my website entitled " A spark erosion apparatus" that I hope is of interest to this discussion, see:
Mike
28/03/2011 23:25:43
Hi Jeff,
Thanks for the comments. Try this link:
28/03/2011 21:14:04
I am currently building a spark erosion machine of the solenoid type based on this design:
 
 
The erosion rate of the unit, as published, is not high because the capacitor charges through the solenoid which has significant resistance and this limits the oscilation rate of the armature.
 
I have considered using a 555 timer to contol the oscilation rate and then supplying the tool with current from an independent supply. The problem with this approach is that the the pulse supply to the solenoid is critical. If it is set at too high a repition rate then the capacitor does not reach full charge. In addition the pulse duration is critical if it is too little then the armature is lifted and drops back before the capacitor is charged. If it is too long then the tool spends too long in contact with the workpiece and a lot of current is flowing but no sparking occurs.
 
I have adopted a different approach in that I sense the voltage on the tool. As the capacitor charges up the voltage on the tool rises. When it reaches a certain value then the solenoid turns off, dropping the tool and causing sparking. The trigger voltage can be varied by means of a potentiometer. Thus you can choose to operate at a slower speed with a high amount of capacitor charge or a faster speed with a lower capacitor charge. At some speed the current though the tool will be maximum giving the fastest erosion rate.
 
This is rather a simplistic explanation because there are other factors which influence the repitition rate. As erosion occurs the tool has to travel a greater distance for each oscilation so the frequency changes.
 
The circuit is very simple and I am currently refining it. When the unit is completed I will publish it on my website.
 
Mike
Thread: milling machine power feed
25/03/2011 20:23:34
Hi Dougie,
I have fitted a powerfeed to my X1 mill. I think the principles could be readily transferred to other mills. Futher details are here:
Mike
Thread: O rings
13/03/2011 16:49:31
Most O rings are NBR. Nbr stands for acryloNitrile Butadiene Rubber commonly called Nitrile rubber.
Mike
Thread: casting small parts
09/03/2011 21:27:00
Hi Keith,
I agree that the fine structured styrofoam is much better than the coarse white packaging foam.
 
I am intrigued by your statement that you can buy the fine structured stuff at a builders merchant. All I can get from a builders merchant seems to be the right stuff but aluminium foil coated on both surfaces. On top of that they only sell in 2.4 x 1.2 sheets. Do you have the name of the product and the names of any suppliers?
 
On the question of porosity aluminium dissolve hydrogen when it is hot. The hydrogen comes from water in the furnace gases. Water reacts with aluminium to produce hydrogen and aluminium oxide. On cooling the hydrogen comes out of solution creating porosity. The swimming pool tables contain either chlorine or bromine (not fluoride) and this scavenges and reacts with any dissolved hydrogen eliminating it from the metal.
I have tried using Lo Salt (made for people on low salt diets) as a flux. This melts at a lower temperature than common salt (it is actually a mixture of sodium chloride and potassium chloride). It is very effective in ridding the molten metal of dross. This all floats to the surface as a greyish powder that is very easy to scape of with a drossing spoon. I have also recently tried sodium bicarbonate (baking soda) but this seems to provide little benefit.
 
With regard to crucibles I use stainless steel canisters. Unfortunately many of these are very thin and do not last long. It is better to pay more for something made with thicker guage material. I buy heavy guage stainless steel mugs in Portugal which seem to last for ages, Unfortunately I have not found a supplier in the uk.
I also find that if you heat a new stainless steel vessel for some time to red heat to form a good layer of oxide on it then this insulates the metal from the molten aluminium and the vessel then last a lot longer before perforation.
Mike
Thread: Which silver solder
09/03/2011 10:32:35
Hi Eric,
I would use Easyflo 2 and Easyflo flux.
Mike
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