advice needed

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jayell
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advice needed

Postby jayell » Fri Aug 08, 2014 9:11 am

I am in the process of converting a 3 phase bech drill to 2 phase and am wondering if I can safely use the original rotary switch for the single phase supply. The switch has 3 connections on the 'input' and 2 on the 'output' side plus an earth connection. Only 2 of the input connections link to the output ones when the knob is rotated from off to on but what worries me is that there seems to be a measurable resistance between the input side to earth in the on position which is not there in the off postiion.

I know nothing about 3 phase wiring so have no idea what in happening in the innards of the switch, the only reason for using the original switch is
a) it is already in place
b) I haven't managed to find a suitable alternative on the web.

John Lewis
(I should have taken a photo but don't have time to do that right now as I'm about to take my wife to visit her disabled cousin in Salisbury.)

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grovenor-2685
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Re: advice needed

Postby grovenor-2685 » Fri Aug 08, 2014 9:27 am

Where are you getting a two phase supply from? And how are you going to run a motor on it? I have only come across domestic 2 phase supplies in Australia.
If this is really a 3-phase drill all 3 phases would be connected to the motor, which does not tally with your description of the switch.
Keith

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Guy Rixon
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Re: advice needed

Postby Guy Rixon » Fri Aug 08, 2014 9:58 am

Sounds like a single-phase motor rigged to work off one phase of a 3-phase supply. I understand that this is common practice in workshop tools; where I worked a while ago, the mech workshop was set up like that. Only hugely powerful motors need to connect to all three phases, and a bench drill isn't int that category.

If this analysis is correct, then you should be able to use the switch as it is, connecting single-phase live and neutral to the input side of the switch. However, if it's something more subtle, then it would be unsafe to connect it thus. You might wreck the motor, and you could cause a safety hazard. Please note also, that I am not a qualified electrician, and my advice is not sufficient to proceed, even if you're sure that it actually is a single-phase motor. You need to check with someone qualified.

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Simon_S
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Re: advice needed

Postby Simon_S » Fri Aug 08, 2014 11:23 am

Hi John, I did do what you hope to do but learnt that using a rotary switch is bad practice. Get yourself one of these:No Volt Release Switch
This ensures that the machine will not restart after a power interruption until the go button is pressed again.
Regards,
Simon

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Guy Rixon
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Re: advice needed

Postby Guy Rixon » Fri Aug 08, 2014 11:26 am

Thought again. In more detail, it sound like your device is wired to run a single-phase motor on the voltage difference between two phases of a three-phase supply. This replaces "run on one phase of a three-phase supply" and I still think it's the arrangement used in my old job. Therefore, would probably work on live and neutral of a single-phase supply.

HOWEVER: you also need to consider what voltage the device expects, 3-phase commonly being 415V.

jasp
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Re: advice needed

Postby jasp » Fri Aug 08, 2014 5:13 pm

" HOWEVER: you also need to consider what voltage the device expects, 3-phase commonly being 415V."

Yes, but each coil only has 230/240 across it.
There are several different types of motor designed for three phase working. Speak to someone familiar with such motors for definitive advice

Jim P

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jayell
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Re: advice needed

Postby jayell » Fri Aug 08, 2014 7:08 pm

grovenor-2685 wrote:Where are you getting a two phase supply from? And how are you going to run a motor on it? I have only come across domestic 2 phase supplies in Australia.
If this is really a 3-phase drill all 3 phases would be connected to the motor, which does not tally with your description of the switch.
Keith


Oops! I should have written 'single phase domestic supply' I have replaced the original 3 phase motor with a similar design single phase motor, I had to find a 'similar design' motor due to the way it is mounted on the drill

John Lewis

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jayell
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Re: advice needed

Postby jayell » Fri Aug 08, 2014 7:19 pm

Simon_S wrote:Hi John, I did do what you hope to do but learnt that using a rotary switch is bad practice. Get yourself one of these:No Volt Release Switch
This ensures that the machine will not restart after a power interruption until the go button is pressed again.
Regards,
Simon


I suspected on elf and safty grounds that I ought to use a no volt release switch as used on most bench drills these days, but was trying to use the switch built in to the base. It really needs me to provide a photo so you can see why I wish to do that. However I could mount the modern switch onto the motor itself where the mounting plate would normally be so have ordered a switch from axminster tools


John Lewis

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jayell
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Re: advice needed

Postby jayell » Sat Aug 09, 2014 9:10 am

johnlewis wrote:. It really needs me to provide a photo
John Lewis


so here are four pics taken this morning whilst waiting for my wife to get ready to go to Wells ;)

first one is an overall view of the drill, showing how the 'ancient' hoover 1/4hp motor is mounted vertically using the four through case bolts. It pivots around the bolt in the lower casting to provide belt tension. I plan on using 5 or 6mm round plastic belting instead of the oversized v-belt that was on it when I got it. I had to open out the bore on the three step pulley from 1/2" to 5/8" so the lathe in the backgound came in very usefull. In fact that job was one of the reasons I got the lathe in the first place :D
benchdrill01.jpeg
benchdrill01.jpeg (254.92 KiB) Viewed 4859 times


number two shows the usual mounting position with the mounting plate removed, the new switch will be fixed to that and plate re-installed
motormountingplate.jpeg
motormountingplate.jpeg (212.57 KiB) Viewed 4859 times


number three shows location of current switch in base casting. The small switch originally operated a 12 volt bulb mounted above the drill chuck but the bulb holder and wiring is missing, power supply for that came from a hefty transformer installed in the base.
switchlocation.jpeg
switchlocation.jpeg (218.14 KiB) Viewed 4859 times


and last pic shows the rotary switch inside the base casting, the power cable will now be removed and fed into the appropriate hole in the new 'no volt' switch
existingswitch.jpeg
existingswitch.jpeg (258.88 KiB) Viewed 4859 times


One big advantage of this design of drill is that the quill does not move up and down so nothing to wear there and there is no play at all in the bearings, the small jacobs chuck, I think the max capacity is about 3/16" so ideally suited for the size holes we need to drill for 4 mm scale stuff, also runs true. The table is raised and lowered by the lever in front and has a rachet to make it easy to position, the lifting ram is also unworn so all in all I think it worth the £40 it cost me, plus another £25 for the replacement motor and now £16 for the new switch.
I spent over £40 on a bench drill attachment for my dremel only to find it nearly useless for doing accurate drilling

Just in case anyone wonders there is a cover to enclose the drive belt, but I have left it off for now.
John

Terry Bendall
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Re: advice needed

Postby Terry Bendall » Tue Aug 12, 2014 6:11 am

johnlewis wrote:I know nothing about 3 phase wiring so have no idea what in happening in the innards of the switch


In which case, despite the well meaning advice on here, my advice would be don't touch it and get someone with the right knowledge to do the job.

Terry Bendall

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jayell
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Re: advice needed

Postby jayell » Thu Aug 14, 2014 12:16 pm

Last posting to this thread (I hope), no need for me to get involved with 3 phase electrics thanks Terry as I have now fitted the no volt switch I got from 'Axminster', the drill is now fully functional and here is a piccie:-

drill_with_new_switch.jpeg
drill_with_new_switch.jpeg (357.98 KiB) Viewed 4641 times


I used one of the cheap taps I got from China to tap 4 fixing holes for the switch case in the mounting plate, got a pack of female spade terminals and some heat shrinkable tubing from Maplins to make neat connections inside the case and put it all together in about half an hour.

I will need to make up some sort of mounting jig to fix to the drill table, probably a bit of 6"x4"x1/4" aluminium or brass sheet with lot of 4BA or equivalent metric tapped holes in it, plus an assortment of fixing dogs. Things small enough to hold wagon buffer beams so I can drill holes for buffer stocks etc.

Now to find a source of suitable sheet ally or brass :)

John

Terry Bendall
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Re: advice needed

Postby Terry Bendall » Fri Aug 15, 2014 6:18 am

johnlewis wrote:I will need to make up some sort of mounting jig to fix to the drill table,


It is of course always important to make sure that anything being drilled is held firmly. However for much of what is likely to be done in 4mm scale, and come to that in 7mm, bolting things to the table is unlikely to be needed. When needed I use a hand vice for thin sheet material, see http://www.chronos.ltd.uk/cgi-bin/sh000 ... ehtml#aHV2 and for small but thicker items a machine vice, see for example http://www.chronos.ltd.uk/cgi-bin/sh000 ... aXC3345_2e

Terry Bendall

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jayell
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Re: advice needed

Postby jayell » Fri Aug 15, 2014 9:30 am

Terry Bendall wrote:
It is of course always important to make sure that anything being drilled is held firmly. However for much of what is likely to be done in 4mm scale, and come to that in 7mm, bolting things to the table is unlikely to be needed. When needed I use a hand vice for thin sheet material, see http://www.chronos.ltd.uk/cgi-bin/sh000 ... ehtml#aHV2 and for small but thicker items a machine vice, see for example http://www.chronos.ltd.uk/cgi-bin/sh000 ... aXC3345_2e

Terry Bendall


It is important to remember that fingers are _very_poor_ work holding tools and that any part being drilled should be held mechanically in some way. Drill press vices come in various sizes and designs and I already have a fairly cheap vice on my 1/2" bench drill but the table on that drill is slotted making it easy to fix the vice to the table to prevent that moving should a drill 'grab' in the work piece.

Parts being worked on in 4mm scale sizes are unlikely to cause that sort of problem and it is probably more important to stop the workpiece from moving to prevent drill breakage which is always a potentional problem with drills of 0.5mm dia or smaller. So a small drill vice is on my 'needs' list, with this one currently on top of the list
http://www.axminster.co.uk/50mm-quick-release-vice, but a smaller one would be better.

I am fairly sure I have seen description of a drilling fixture of the sort I am thing of in one of the many Model Engineering Workshop Practice books I have read over the years but soemthing like this tooling plate but on a smaller scale is what I am thinking of.
http://www.sherline.com/3560inst.htm

There may be a commercial product available from a clockmaker's tools supplier but I haven't found one yet so making one is the obvious way to go. The grid of holes doesn't need to be too precise and the fixture should be thought of as a 'throwaway' device as inevitably the surface will end up with spurious holes in it.

My precision drill doesn't have the conventional slotted table but does have four 'half slots' I can use to hold a drill fixture in place and the tapped holes in the fixture can then be use to hold various locating fences, holding down dogs etc in position.

Making tools like this will delay the production of the railway models I am working on and I am sure many people will just get on with the model making and not worry about too much about making jigs and tools first but I like the toolmaking aspect as much as making the end product, ie a 4mm scale railway wagon, coach or loco (and the parts aren't quite so small)

John

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Tim V
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Re: advice needed

Postby Tim V » Fri Aug 15, 2014 12:49 pm

A plate similar to the Sherline product used to be produced by the 2mm Association, but it's no longer listed.
Tim V

billbedford
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Re: advice needed

Postby billbedford » Sat Aug 16, 2014 7:39 am

If you are drilling thin metal, better than any of these fancy bits of tooling, is an offcut of hardwood floor boarding. You can dog your work to the timber and still have the flexibility to move the work around to pick up multiple holes.
Bill Bedford
Mousa Models
http://www.mousa.biz

Terry Bendall
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Re: advice needed

Postby Terry Bendall » Mon Aug 18, 2014 8:03 am

johnlewis wrote:It is important to remember that fingers are _very_poor_ work holding tools and that any part being drilled should be held mechanically in some way.


This depends on the material being drilled, the size of the work, and the size of the drill bit. A 3mm dia hole on a piece of timber say 300mm long x 45mm wide x 2mm thick could very easily be held with the hand whilst drilling is bing done.
When I was teaching I would be quite happy to see this being done by one of my pupils.

A 3mm hole in a piece of mild steel 10mm square and 4omm long is an entirely different propostion and in which case the work would be held in a machine vice and the vice clamped or bolted to the table of the drilling machine.

If I needed to drill a 6mm diameter hole in a piece of acrylic 3mm thick I would probably clamp that down, since unless the point able of the drill is changed from the normal 118 degrees to something more like 125 degrees, the drill bit will often snatch. The same would be true when drilling a hole of say 10mm diameter in thin sheet metal which i would always clamp down.

After 58 years of using drilling machines of all sorts of sizes I have a reasonable idea of what I can do. Those with less experience would be well advised to clamp or fix the work in some way for most situations but for much of what we do in 4mm scale using a hand vice, or a small machine vice held with one hand will often be sufficient.

Terry Bendall


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