Dewhurst switch parts wanted

Yes Ken,

If you had searched for Dewhurst in the newsgroup you would have found I was offering Dewhurst parts to people only a month ago - but there were no takers - so I threw them out !

Only kidding ..... I put them to one side. I knew that if I threw them out then someone would want them.

I rebuilt one good switch out of two dodgy ones - an old brown faced one with copper rollers, and a newer blue faced one with steel rollers. I re-used the copper rollers as the steel rollers were burnt, though some more than others. I have spare blades too, and have posted pictures of the wiring diagrams on the web (see previous thread for links).

Drop me a line - e-mail to oldnoccer at btinternet.com

Steve, Cheshire

Addendum

I have moved the Dewhurst wiring diagrams around. New location is

for anyone having problems wiring one up.

Steve

Hi Steve, taken me ages to find someone like you who has rebulit a dewhurst switch, I decided to strip my switch completley, blast, cadmium plate and repaint all the steel work, and just give the contact pins a clean up, unfortuanately I assumed there was 8 contact pins in the switch, but there are 4 short and 2 long, so when I dismantled it all the pins came away from the black holders, and I just dont know in what position they go back together.(Would new brass pins be ok to use instead of the original steel pins,I have access to brass bar or stainless steel) Is there anyway you can check your switch to find out what order the pins go back into the holders, starting from the off position working down the switch is it a short or long pin etc. (you have to remove the spring clips to use a multimeter to "bell out " each pin Photos would help or a sketch Regards Sam

You can email to snipped-for-privacy@utvinternet.com or I can phone you if you like (might be expensive you phoning me as I live in N.Ireland

Hi Sam,

I think you can find all the clues you need in the diagram labelled switching arrangement on the web page

- its not just an electrical diagram, it actually shows the layout of the switch.

If you place your switch the same way round as in the diagram and switch it to the forward position you will see that on the left there should be a long pin bridging terminals 1 and 2, and short pins for each of terminals 3 and 4. On the right of the switch there should be a short pin on terminal 5, a long pin bridging 6 and 7, and a short pin at terminal 8.

Note that the spring clips that connect across the switch left to right are also shown in the diagram. There are three of them, don't put them in the wrong place or you could have a dead short. After assembly always check with an avo, don't go straight for the mains supply ! The connections should work exactly as in the diagram regardless of what you plan on connecting it to - though pins 4 and 8 are not used for a simple single phase motor - so you have some spare contacts there.

As for materials for the pins, I don't think the switch is too fussy. Later ones had steel pins, early ones copper. If you use the switch while the motor is off (i.e. use a separate on/off switch and don't switch it under load), then I don't suppose you will have a problem.

Steve

Sam Haylock wrote:

Hi Steve, many thanks for that, I take it from the diagram you bridg

pins 1-5,3-7 and 4-8 with the spring clips. When the switch is in the OFF position is there supposed to be a lot o "play" in the ON/OFF lever (may have got the tension spring/arms fitte wrong), do you know what way the tension spring is fitted to the arms, seems to be quite a gap between the square on the plastic holde and the 2 arms, which causes the excess "play" I thought the 2 arm should be nearly touching the square, so it would stop the "play" i the lever. I think I have all bits fitted that I took apart. I shall get the switch checked out with a sparky at work, he is goin to work out all wire positions .

Sa

-- Sam Hayloc

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Yes, no shorting link between 2 and 6, that would lead to a dead short between input terminals 1, 2 and 3 - which would be a bad idea !

No, there shouldn't be a lot of play, so you probably have the arms set wrong. When I stripped mine I took a couple of photos to help me put it back together, but I don't think they came out well enough to see this detail. I'll have a look and get back to you.

Do him favour and provide the wiring diagram from the website, that way he won't have to work out the wiring positions on the switch - though you should probably offer him the motor too. Diagram 1 is the most common, thats for most single phase motors, but if you have three phase then there are others to choose from. Note that this sort of switch is not allowed any more due to some European directive or other, which is why you can't buy a new one. Your sparks may raise that.

Hi Steve, way ahead of you this time , the sparky has had the motor o

his desk at work for a week or more waiting until I get the pins sorte out (which you done for me) and I have printed the wiring diagram fo him, he checked the switch out before I stripped it down and he wa happy enough with it,(he wasnt aware I was going to strip it down) I a also getting a few new labels, my original was badly damaged (jus need 1 but just as easy making a few extra when machine is set) mad out of aluminum alloy, just OFF, FORWARD/REVERSE engraved on them anodised and dyed blue ( I can get this done at work) Anyway hope your photos come out ok.

Sa

-- Sam Hayloc

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As I suspected the photos are marginal, so I whipped the cover off the one I rebuilt. Going from the outside inwards we have the screw head and washer, the insulating bar that carries the contacts, then the bracket which is part of the base-plate, then the nut, and then the spring 'lever' goes over the remaining part of the screw thread which is sticking inwards towards the centre.

This means you can do up the screw and nut before fitting the spring levers and spring. It also means the spring lever simply pivots on the end of the screw thread rather than being clamped by the nut.

Steve

Hi Steve,many thanks once again,I done a mock up before final assembly

got it sorted, I had all the bits but not necessarily in the righ order, I had screw head-contact support-spring arm-washer-nut. I was just checking the wiring diagram again, in the forward positio should the knob be at the left hand side in line with nos. 1,2,3, (left hand view on diagram) and on the right hand side in revers position.Looking at my switch the nos. 1,2,3.4 are in line with th word FORWARD on label ? I am just waiting to get my new label engraved with all origina markings then anodised and dyed blue, and fill engraved characters wit white wax.

Best regards Sa

-- Sam Hayloc

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No, the opposite.

Correct

The normal lever screws through the switch spindle and leave a short stub to point to the word on the face. So the diagram is correct, the ball is always furthest from the selected position.

Sounds like you are making a job of it. I hope whatever you are switching on and off appreciates it.

Steve

Hi Steve, I bought my switch on ebay, and I have just looked today unde

"myford switch" on ebay and seen the actual lever on the origina switch.Look on ebay with this no. 7629448307. Now that I see origan lever its all becoming a bit clearer My switch does not have the original lever (but I will get one made i the next few days) there is a boss fitted over the end on my spindl and a lever welded at about 45 deg. then the knob is screwed on th end.The boss is held in position with a grub screw at 90 deg to thread through spindle. Does your switch have origianal lever fitted ?, if so any chance of th size of it, lengths/dias. etc. I can check thread size at work on m spindle if your not sure of it. I should be able to get a new leve made at work in the next few days. Many thanks again for your time and help.

Best regards Sa

-- Sam Hayloc

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