Would anyone be kind enough to scan and email me the Rawlinson articles from
these issues of MEW on the bandsaw butt welder and related spot welder
If the files are a bit big then maybe they could be temporarily uploaded to
an ftp site instead.
Nice big mailbox at this address.
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.
Norfolk - UK not VA
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
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
Good Luck and do let me know how you are getting on.
Happy New Welder (Year)
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.
secondary is on
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.
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 & Rita Forbes
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
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?
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
Peter & Rita Forbes
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
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 & Rita Forbes
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.
Visit the new Model Engineering adverts page at:-
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
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)
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