MEW 41/42

Thanks to JS, I now have the file.

Bob

Hello Bob, Snap. I'm looking to build one as well. Other than finding a supply of the xformer, looks easy enough. Have posted a request for help on supply. Happy New Year.

GeoffH (The Pirate) Norfolk - UK not VA

Hi Geoff, I'm about to commission a band saw into my new woodworking workshop and had been considering buying bladestock & self welding or paying the extra for ready made blades. The MEW design is quite expensive on components when you start totting it up. I think I would have to weld an awful lot of blades to justify the cost. But it would be an interesting project nevertheless. I've got a couple of years till I plan to retire when there should be more time but for now I fear this will stay on the roundtoit pile.

I've got to complete the workshop yet - I started last boxing day building the roof and so far I have 30 sqm, warm, dry and well lit and some machinery and on the lookout for more. Layout planning and power wiring are next on the list followed by dust extraction.

I'd be happy to stay in touch and kickaround any issues you have with the welder. The tranny is the biggest problem as you say. Modern ones are vacuum impregnatedso look out for older specimens ideally where the secondary is on a separate section of the bobbin and easier to remove without risking damage to the primary. At least with this requirement, the iron stack does not need to come apart to wind on a few turns for the secondary.

The other idea I have is to canibalise a Variac. Many are rated at 8 amps/2kva which is plenty. Remove all the variable stuff /brushgear until you are left with the core and the all important winding. There is a terminal at each end to connect to the mains.

The 8 amp ones are usually about 1 turn per volt so you wont need many turns for your secondary. You can assess this either by counting or just wind a few turns of secondary with light gauge wire and measure the voltage developed. Try to get multistrand cable - as many strands as possible - for the working secondary. It will be so much more flexible. Welding cable is ideal or a few pieces of starter motor cable (equal lengths) in parallel would be a good substitute. For intermittent duty use you could easily run the secondary at

4000 amps per square inch maybe more if you are fan cooling. The weld time will quite short which is when all the current will flow, the annealing current will be quite a bit lower. Consider a few layers of gaffer tape or other good quality cloth based tape around the primary before you start A piece of tufnol attached to where the rotary mechanism used to fit on should give you somewhere to bring out the connections and then re-use all the shrouding to provide some element of safety.

I'm assuming you are generally OK with electrics to be contemplating this project anyway.

Good Luck and do let me know how you are getting on.

Happy New Welder (Year)

Bob

Bob -

I am also contemplating having a go at this project. Any mileage in cannibalising old stick welders to create the necessary tranny? I have a very nasty old SIP welder in the garage that is probably destined for the scrap man unless it can be used for something like this.

Regards, Tony

secondary is on

risking damage

voltage

Tony,

The blade welder on my Startrite bandsaw is VERY much smaller than that in a welder. Don't forget it only needs to be intermittently rated. Actual welding time may be 5 seconds and anealing time maybe

10-15 seconds and then is will rest for ages before you do another.

AWEM

What are the actual ratings required?

We probably have enough large laminations left to make a couple up, but need to know what output is required?

We don't wind much large stuff now, but still have plenty of enamelled winding wire up to 3mm diameter, and bobbins and frames.

Peter

-- Peter & Rita Forbes Email: snipped-for-privacy@easynet.co.uk Web:

Should be be more than adequate for the job. The ease of use comes from the detail of the welder tranny construction and the size of the core as this will have to be close to the butt welder business end due to cable size/losses.

hth

Bob

The author starts by aiming at 1Kva and then in the text talks of lower powers 250 to 300 va. It depends a bit on the max blade size obviously but he reckons 300va will do 3/4" x0.024" bladestock. He ends up using a custom tranny from an undisclosed supplier.

I guess that Tony as a fellow contributor to MEW might be able to get more info from the author?

Regards

Bob

Thanks, Bob.

That can be 1000A at 1V or 1A at 1000V or something in between!

If you work on something like 2.5V at 350A with a 1/10th duty cycle, you'd probably get something like that from a 638 or 750 frame size quite easily.

I know we have a big low voltage plating transformer lurking somewhere, that is continuously rated at 300A 5V DC output after rectification and smoothing, but it is enormous and is being saved for some electrolysis experiments :-)) That is on an 825 frame size (638 frame is about 6" X 5" lamination size, 750 is about

8" X 6" and 825 is about 9.5" X 8". I have the Linton & Hurst lamination catalogue around here somewhere at home, but haven't used it for yonks, so I'll check the proper sizes on Tuesday.

I'll speak with our tranny designer on Tuesday and see what we can concoct between us.

Peter

-- Peter & Rita Forbes Email: snipped-for-privacy@easynet.co.uk Web:

Hi Peter, I did not mean my quoting Kva alone to be unhelpful.The author is working below 1 volt both 0.6 and 0.7 are mentioned in the text and because he had arranged for a supply of the transformers, the final spec for this and many other components in the design are just referred to as " order part no abc123 from supplier no 4". He quotes himself as the tranny supplier!

I will forward the article to you so you can see our common start point.

I'm sure the potential builders in this NG will be grateful for any light your transformer designer can shed on the project.

Happy New Year

Bob

No problem, I just wanted to try and get a starting point for a possible design.

Got the article, many thanks, I'll have a read through.

Certainly less than 1V output would cause volt drop problems in the connections, so best to start a little higher I'd have thought.

We do have a new reel of 10mm X 2mm enamelled as well, might be worth looking at that instead of round wire. We never used it, so it would be nice to find something useful to do with it rather than gathering dust!

Peter

-- Peter & Rita Forbes Email: snipped-for-privacy@easynet.co.uk Web:

Weight the bugger in and buy a blade welder

Somewhere kicking about here I have a proper bandsaw welder but it's a

3 phase model. I can dig it out during the week and plug it in to see what voltage it throws out if that will help.

Also thinking about it I have two trannies that have 240 volt input and three 11v outputs at 50 amps per winding so that would give 50,

100 or 150 amps if you paralleled the windings up.

No idea if these are suitable but they came out of a big CNC stepper drive and are working. Given size and weight they would have to be buyer collects for the usual beer vouchers.

-- Regards,

John Stevenson Nottingham, England.

Visit the new Model Engineering adverts page at:-

Gentlemen,

Near where I live we have a company called THE BEDFORD SAW COMPANY who supply, make and sharpen all kinds of saws including Band saw blades, made and welded to size supplied, surely a similar company would be an easier and cheaper route.

Martin P

Bob - can I have a copy too please?

I am wondering whether a microwave oven transformer might be a useful starting point? Dud microwaves are available almost for free, and the mains winding of the transformer is highly unlikely to be the kaput-ted part.

The great advantage of these is that they already have a safe mains winding, and you would only (!) have to remove the high voltage winding and replace it with a few turns of thick copper.

(!) assuming an older design with a seperate mains winding, use a chisel to cut off the copper HT wires, being careful not to damage the mains winding, then use a punch to get the inside copper wires out.

Iirc there was an American who built a poky stick welder using 8 of them. But you would only need one for a blade welder.

(an aside - poky? pokey? pokie? can mean powerful, as intended above, or small as in a pokey room. Strange thing, language)

Yikes!

Happy new year all \

-- Peter Fairbrother

The new moon is shining the angels are washing their windows Above the years whose jumble sale goes spinning on below