George Thomas high speed drill.

[Ian P]

On Ian P Said:

I have some less than ideal electrical setups in my workshop but that motor and controller and mains lead being sold on ebay frightens me!

No warnings or advice on the listing to alert the purchaser that the motor wiring is a mains potential. I know there is label about earthing (as in Rod’s reply), but in one of the ebay pictures the earth lead is just shown unconnected.

We know that putting the controller in an enclosure is straightforward but how many buyers will properly protect the red/black motor wires from where they exit the motor endplate to the controller I wonder.

Ian P

I’m in two minds about this.    In general, I’m all for ‘having a go’, ‘learning by experience’ and ‘pushing the envelope’.   But, I also know  the world is full of over optimistic bodgers, chaps who believe in ‘common sense’ when there is no such thing, those who reject ‘Elf and Safety’ on principle, and a large group who are too lazy to read the manual, or lack the basic knowledge needed to understand it.  Beware youtube videos published by proud bodgers, they often include bad practice.

Anyone with a little background in motors and controllers will recognise instantly from the ebay advert that components are on sale, not meant to be exposed in public.    Components are always part of a larger design, and it is this that typically keeps them protected.  100% the responsibility of the designer, that’s us, to get the full design right, not just lash a few parts together.   The danger is that an inexperienced or irresponsible builder assumes an unsafe on it’s own part like that controller is OK out in the open.   A slightly more experienced builder realises components have to be assembled within a safe installation, more work, different skills.

Whether or not a black-box is a component or not isn’t always obvious.  VFDs come in a nice box that looks as if it’s OK to mount the VFD out in the open, with controls the user can twiddle directly.   Nope.   With few exceptions, VFDs are components, meant to be protected inside another box, with externally wired controls.   The display and built in controls are for setting up the VFD up, not day to day use.

The answer I think is to be keenly aware of one’s own limitations.   When a job is ‘different’, something I’ve not done before, I stop and have a think, do some research, and ask on the forum etc.   I’m looking to understand the risks that they can be avoided or mitigated, not to walk away.   If I don’t know what I’m doing, my job is to learn not guess.   Main exception is legal and insurance requirements.

Nanny state intervenes after the authorities have enough evidence to confirm that enough people are up to something dangerous enough for it to be controlled.  The best way of keeping Nanny at bay is for us not cause injury due to incompetent work.

I don’t believe unsafe bodging is common in model engineering – we don’t seem to cause many major incidents.

Dave

 

[Andrew TinsleyParticipant @andrewtinsley63637]

I always thought GHT’s drill was termed a sensitive drill, not a high speed drill. I must consult his book on that.

Andrew.

[Roderick JenkinsParticipant @roderickjenkins93242]

Dave,

A nice, pragmatic and reasonable summing up of the issues.

Thank you,

Rod

[John MCParticipant @johnmc39344]

I built Geo. Thomas’ pillar tool some 43 years ago but have only ever used it as a drilling machine. The first motor was bolted to the bench behind it.  Then I bought a motor from Whiston, (remember his cat?).   This motor, I mounted of the drill itself and arranged it to give two speeds,   approx 3000 and 4000rpm.

This motor has recently failed, needed a flick of the belt to get a reliable start, that’s probably why it failed!  I was hoping this thread might suggest a few low cost alternatives.   Something around 3000 rpm, 1/8 hp would be ideal.  Any suggestions?

The (plain) spindle bearings are showing some wear and will need attention.  I had correspondence with GHT with regard to the bearings chosen for the spindle.  He was keen on plain bearings for the job, dare I suggest he may have got that wrong for this job?  Time to try rolling bearings, needle roller at the bottom, ball race at the top, possibly.

 

[JasonBModerator @jasonb]

The one that was in MEW a few months back that I posted the photo of is 120W so 1/6hp and a quick google suggest smotor and controller will come to less than £40

[bernard towersParticipant @bernardtowers37738]

Needle rollers are not the way to go for this and can you imagine the size the casting would have to be to fit std ballraces in. I personally think well fitting bushes are quieter

[bernard towers]

On bernard towers Said:

Needle rollers are not the way to go for this and can you imagine the size the casting would have to be to fit std ballraces in. I personally think well fitting bushes are quieter

Cannot see why not.  Drawn cup needle rollers running directly on the spindle will take up no more space than the plain bearings.  Lubrication will be less demanding.  As for noise, if there is any it will be drowned by the belt and motor.

I also want to try to speed up the spindle speed, 6000  – 8000 rpm possibly, rolling element bearings will cope much better than plain.

As I previously said, I had some correspondence with GHT over the bearings.  He chose plain bearings because the spindle had to slide through the bearings and wanted to avoid a hardened shaft.

 

[Michael GilliganParticipant @michaelgilligan61133]

On the subject of bearings …

Whilst this is [in every respect] a much bigger project, it may provide some inspiration:

https://www.j-m-w.co.uk/pdfs/HJ-Published-ArticleNEW.pdf

MichaelG.

[derek hall 1Participant @derekhall1]

GHT designed the drilling attachment for the UPT as a “sensitive” drilling attachment rather than a “high speed” drilling attachment.

He does mention drilling speeds in his construction notes, and I believe that the kit that GHT designed is fit for the purpose of the occasional drilling of small holes e.g 3mm dia with a much greater “feel” than attempting to do the same on a giant Fobco bench drill.

If you need a high speed drilling attachment then the GHT drilling attachment may not be suitable. Consequently a different design and motor may have to be used.

In my humble opinion.

[Roderick Jenkins]

On Roderick Jenkins Said:

On Robert Atkinson 2 Said:

On Roderick Jenkins Said:

These motors seem to be back in stock:

hebdenmotorbits on ebay

I use one to drive my lathe toolpost milling spindle and it would fit very nicely on the back of my Pillar tool

 

Rod

 

 

The controller in that ebay listing is deadly. exposed terminals and no earth.At least you put yours in a plastic enclosure.

 

I can’t imagine anybody would consider using the controller naked, if you see what I mean.

Rod

As well as the safety concerns, may I add that this particular speed controller isn’t very good.

I tried one and the torque at low speed was poor. I don’t claim to fully understand the technical reasons but I believe it has something to do with the frequency being very low, it basically pulses on and off meaning you are using a fraction of the motors power.

I have also tried a DC motor with a proper power supply and a separate speed controller which was better but not perfect.

I then tried KBIC style speed controller which are common on Chinese lathes and milling machines. This type is MUCH better. So if you are going down the DC motor route I would suggest this

[Martyn CozensParticipant @martyncozens74564]

Appologies for not replying sooner to everyones answers of help.

The reason a motor mounted on the bench was a faff was that I simply don’t have the room, I just think a motor mounted on the back of the machine would be more conveinient for my purposes.

I had seen the picture of the article in Model Engineer, but my issue is where to source the stuff.

The only reasonably priced option was the one Rod suggested provided it was suitably improved from the safey angle.

Ideally I was  looking for a small AC motor about 200watts, I do have a Parvalux motor which would be fine for bench mounting but its to big to install on the back on the drillhead.

Anyway thank again for everones input.

Martyn C.

[Author]

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