Homemade Grinder Advice

[James Jenkins 1Participant @jamesjenkins1]

[James Jenkins 1Participant @jamesjenkins1]

[James Jenkins 1Participant @jamesjenkins1]

Hi all,

Above should be an initial sketch for a solar powered tool grinder I have started planning and which I intend to use with the Harold Hall grinder rest. I have a 36v solar system and use small motors, originally intended for scooters and go carts around the workshop. I would really like to hear any thoughts on the general set up and in particular on the following:

1. I would really like to use diamond stones, for less mess, convenience and finish. How practical is this? I use HSS and tool steel tools. I have read issues with dressing, but this seems to be more of an issue with surface grinders than bench grinders, with many people simply aligning on a lathe as you would do any addition to a shaft and many others just using them in a standard bench grinder and not worrying about dressing.

2. My intention is to fix the inner grinding wheel flange onto the shaft and then screw the outer one on to this. Thereby removing the need to thread the shaft. Any reason not to do this?

Look forward to all and any thoughts. Likewise any questions.

Many thanks,

James

Edited By James Jenkins 1 on 18/07/2018 14:28:30

[mechman48Participant @mechman48]

No sketch… just a box with a x in it… ?

George.

[James Jenkins 1Participant @jamesjenkins1]

Oh, sorry about that. Here is an alternative server: https://ibb.co/k94E8d

The original displays on my computer. Anyone else having trouble?

James

Edited By James Jenkins 1 on 18/07/2018 14:37:35

[Ian ParkinParticipant @ianparkin39383]

I Would think that you may not have enough power with that motor up it if you can to at least 1/3 hp or 1/2 for best performance

Why not thread the shaft? Don’t try to reinvent the wheel.

If you cant thread it RH and LH i’ll do it for you

[James Jenkins 1Participant @jamesjenkins1]

Hi Ian,

Thanks so much for your reply and your very kind offer, you are right I wouldn't have the capacity to put a LH thread on and that's one of the reasons I didn't go down this route. I also thought that as I would need some sort of flange fixed to the shaft to push up against, I might as well just fix the inner wheel flange. I don't really want to do any turning on the shaft, if I can avoid it, so as to maintain the accuracy of the silver steel, which I am unlikely to match with my turning skills! That was my original thinking, anyway. But perhaps I should go down that route?

The motors come in a range of power ratings, I was simply going off the ones in commercial bench grinders. There are 1/3, 1/2, 1 and 1 1/4 variants, so I will go for something more powerful.

kind regards,

James

[Michael GilliganParticipant @michaelgilligan61133]

Posted by James Jenkins 1 on 18/07/2018 14:37:15:

Oh, sorry about that. Here is an alternative server: **LINK**

The original displays on my computer. Anyone else having trouble?

James

.

The original displays O.K. on my iPad … but it took a second or so to load.

MichaelG.

[Neil WyattModerator @neilwyatt]

You should use fibre or card washers so there is no metal flange to wheel contact, also the gripping flanges are usually cupped so they grip the wheel well away from the edges of the hole.

The centre bore must NOT be a tight fit, which is why a resilient (typically plastic) plug is often used. This helps ensure concentricity. A tight fitting metal plug may expand with temperature and burst the wheel.

Neil

[Neil WyattModerator @neilwyatt]

I found this:

http://www.ccohs.ca/oshanswers/safety_haz/abrasive_wheels/bench.html

The key issues with your design are lack of card washers and no undercut for the flanges, both of which you could incorporate, but I think you also need to check the proportions.

Be aware that the diagram is wrong as it doesn't show the fixing thread extending well inside the flange i.e. you wouldn't be able to grip an over-thickness wheel securely.

Note also that a fixed diameter setup like you propose will only be able to be used with one hole diameter.

Neil

[Frances IoMParticipant @francesiom58905]

the problem with the original image (other than too big for normal displays) is that the hosting company attempts to preload some page prior to the image – blocked on my machine and might well be reason for non display.

However why solar powered ? – a 0.5hp motor would require over 10amps – thick cables ? why not have a dc converter to 250V AC and use a mains powered cheap grinder etc – if you are going to use a diamond wheel then only suitable for touching up and you could get away with a small aluminium based hispeed wheel that might be more suitable for a dc motor – you only need higher power if you intend to hack away HSS cutters and for this purpose the standard grinding wheels offer a much lower cost than diamond wheels.
You might also be better off to use 12mm rod rather than 0.5″ as 12mm metric lh nuts are considerably cheaper that old imperial – if you look at H Hall’s book which includes the grinding rest he has a suggestion of truing up a cheap grinder and then gluing a back plate to shaft and truing up the backplate by setting the grinder up on a lathe.

Edited By Frances IoM on 18/07/2018 15:52:17

Edited By Frances IoM on 18/07/2018 16:14:12

[James Jenkins 1Participant @jamesjenkins1]

Dear all,

Thank you so much for your advice, particularly with regard to mounting the grinding wheel – I will take these into consideration. Yes, Frances you might well be right with regard to using 12mm – I am more set up for imperial and so just tend to automatically design in that way. This is just an initial rough sketch, so that could be changed easily.

My intention is that initially there will be some more serious grinding, as I get together a set of good HSS lathe tools, but that from then on it it should be touching up more than anything, making it as easy as possible to ensure that it gets done regularly. I guess one option would be to put a standard grinding wheel on one end and a diamond on the other. How often do people find that they have to use a cup wheel? Initially it will be lathe tools and drills for me, with end mills and other basic milling cutters soon after.

The solar system that we have is all low voltage DC, for lighting, machines etc. I debated long and hard which way to go with it, but decided in the end on the current setup – for better or worse now – and I have to say it works well for our needs.

Many thanks for your helpful feedback so far.

Kind regards,

James

Edited By James Jenkins 1 on 18/07/2018 17:05:08

[SillyOldDufferModerator @sillyoldduffer]

Just a thought but are scooter type DC motors fast enough? ( The only one I looked at had a built in gearbox to drop the rpm. ) Grinders spin quickly, say 1500 – 4000 rpm depending on wheel diameter. Might need gearing back up.

The other issue might be how much work you intend doing on the grinder. My cheapo 3/4HP bench unit is rated S3 ie:

S3 Intermittent periodic duty. Series of identical duty cycles each a constant load for a period, followed by a rest period. Thermal equilibrium is not reached during the cycle.

It's OK for sharpening a few tools, but the motor heats up after about 10 minutes and soon has to be rested. It's important not to overheat it. I expect a golf cart / scooter motor would be rated for continuous operation but check the plate.

The part that really makes a difference to a grinder is the bit you haven't designed yet! It's the platform thingy you rest the item on while grinding it. Most modern grinders come fitted with a nasty rest made of bent tin-plate and are much improved by being stiffened up.

I recommend fitting a guard. At 3000 rpm the outer edge of a 6" wheel is travelling at over 50mph and grinding wheels have a reputation for disintegrating. Also not a good idea to touch a turning wheel with your hand.

Dave

Edited By SillyOldDuffer on 18/07/2018 17:19:17

[Robert DoddsParticipant @robertdodds43397]

James,

Your sketch shows no detail of how you intend to fix the inner flange to the silver steel shaft and this is one of the most important points in mounting grinding wheels. A pinch screw on the inner flange is not adequate. The flange will tend to run out of true and the prospect of it coming undone is unthinkable!! Adhesive fixing is equally unacceptable.
There is plenty of online data and regulations regarding mounting grinding wheels. Have a look at those before making something that can be lethal.

Regards Bob D

[James Jenkins 1Participant @jamesjenkins1]

Hi,

Thanks for the replies and advice.

The DC motor runs nominally at 2,800rpm, but obviously being DC can easily be slowed down (actually our system voltage is over 36v, so it will naturally want to run a little quicker, hence the importance of the PWM to slow it down).

As mentioned the platform will be Harold Hill's simple one, in Tool and Cutter Sharping, which is where I got the very basic outline for the flanges from. I appreciate they are very basic, as I wanted to get feedback on what would and wouldn't work on these and the strong consensus seems to be that these should be of typical construction, with a threaded end and inbuilt flange on the shaft for retaining.

Looking at tool and cutter grinders, such as the Quorn, Vertex, Worden – I see that most are a single wheel design, much smaller than the 6" standard bench and I wonder if this isn't something to look at and throw into the mix and could simplify the design (i.e. no need for a left-handed thread)

I had intended to guard the wheel and pulley, again not shown on this initial diagram, most likely with a polycarbonate shield.

I would be really interested to hear if anyone is using diamond wheels for tool sharpening?

Many thanks for all this feedback – very much appreciated.

James

[john carruthersParticipant @johncarruthers46255]

Yes, I use a diamond wheel for tool grinding, mainly carbide tools but most things in my shed get a touch at some time.

Have you looked at the battery powered grinders available..? maybe something could be adapted?

**LINK**

We had a little homemade grinder 'out the back' in our old works, it was rescued from a skip.
It was made from a Picador spindle and a little 1/4 hp motor, only took 4" wheels.
The main problem was keeping grit out of the bearings, the shaft rattled around like a stick in a bucket.

[Michael GilliganParticipant @michaelgilligan61133]

James,

If I may digress slightly: This seems a good time to mention a clever device that was featured [decades ago] in Model Engineer.

Small hand-cranked grinders were available at the time, and the ingenious author had grafted a bicycle freewheel unit onto one of these … with a length of bicycle chain, a simple hinged treadle, and a return spring.

Food for thought in your situation ?

MichaelG.

.

I can't be sure, but … searching the ME index suggests that this may be the article:

1934

70

1729

612

Ernest Morrison

A Treadle Attachment for a Hand Grinder

Edited By Michael Gilligan on 19/07/2018 09:25:13

[Neil WyattModerator @neilwyatt]

Another word from Cassandra – back in the day before cheap bench grinders MEW was always full of people suggesting using DC and 'universal' motors to make grinders.

These articles were always guarded with reminders about the hazards of overspeeding grinding wheels with non-synchronous motors.

It was, I think, 'Duplex' who presented a grinder with a friction pad to stop a grinder overspeeding with no load, probably one of the dodgiest designs ever featured in the 'hallowed' pages of Model Engineer.

Neil

[HopperParticipant @hopper]

Posted by James Jenkins 1 on 18/07/2018 15:21:01:…

…I wouldn't have the capacity to put a LH thread on and that's one of the reasons I didn't go down this route. I also thought that as I would need some sort of flange fixed to the shaft to push up against, I might as well just fix the inner wheel flange. …

This looks like a bit of a shortcoming in your design. IIRC you have a Drummond M-type? If so, left-hand thread is a simple matter of adding an extra change gear into the gear train, mounted on a stud on the forked casting that sticks out of the headstock at the left-hand end. No need for reverse spindle rotation or any of that.

It is more usual on grinders to make the main spindle a bit larger diameter then turn the ends down to 13mm/half inch, thus making a square shoulder for the wheel flange to locate on. You could use a piece of 17mm bar with standard 6203 bearings, or even go up to 20mm. The half-inch/13mm diameter shaft all the way along could be a bit thin and flexible for the weight of the wheels at each end, specially if a wheel becomes out of balance or loses a chunk in one place during accidental rough use.

You'll also need something to locate the spindle lengthwise in the bearing pedestals. Usual method would be to use a piece of 20mm shafting, turn it down at each end to fit the 17mm ID of a pair of 6203 bearings then turn the very ends down to 13mm/half-inch to fit the holes in the wheels and thread to suit. The 17mm shoulders locate the spindle in the bearings. The 13mm shoulders locate the wheel flanges. Simples but effective. And stronger than a long half-inch shaft right through.

Also, why use a round belt? A common V belt will slip less under load and wear better. Round belts are more commonly used on toolpost grinders where cuts in tenths of a thou generate very small loads compared with grinding toolbits offhand.

Edited By Hopper on 19/07/2018 09:44:44

[Ian S CParticipant @iansc]

Actually thin flat belts are thought the best for tool post grinders. I would agree with Hopper about going up in size for the shaft, you probably wouldn't need anything more fancy than BMS. Good sealed bearings possibly with some sort of extra cover over the outer face of the bearing, the the grinding grit gets in every where.

The first powered grinder I had for sharpening lathe tools had a wheel about 2" dia, and driven by a motor of about 60W, it started life as a combined electric can opener, and knife sharpener.

Ian S C

Edited By Ian S C on 19/07/2018 10:20:13

[James Jenkins 1Participant @jamesjenkins1]

[James Jenkins 1Participant @jamesjenkins1]

[James Jenkins 1Participant @jamesjenkins1]

Hi all,

Thanks so much for your feedback and advice, which has been absorbed into the update and refinement of the drawing. Still only draft at this stage (I won't be making it until most likely September).

The guards I will either make out of polycarbonate or a built up wood veneer. I want to experiment with both techniques and see which works best.

The flanges have been worked up, using the advice from here and the drawings in Harold Hall's book.

All and any thoughts and suggestions welcome (as I am sure you will know, right clicking and selecting "View Image" will let you see the drawings much greater detail).

James

Edited By James Jenkins 1 on 20/07/2018 15:10:31

[HopperParticipant @hopper]

Yeh, looks more solid. Will need something to locate the spindle endways in the bearings. Either steps on the spindle or collars and grub screws up against the bearings. Not sure you would need the M4 screws holding the two flanges together. The nut on the spindle usually provides the clamping force.

I really must teach myself CAD sometime. The drawings do come up nicely. What program did you use to draw these ones?

[James Jenkins 1Participant @jamesjenkins1]

Hi Hopper,

The collars on the bearings have grub screws built in – I sort of assumed two of these would be enough, but maybe a collar up against the rear bearing, given most of the force will be inwards would be sensible.

I use Adobe Illustrator for the drawings, not true 3D CAD, in that each elevation has be drawn separately and you cannot do the fancy 3D trickery, likewise drawing out the internal features etc etc I suppose it's more electronic drawing really, lines and circles built up etc. CAD would be much more sensible, but I know Illustrator quite well and don't fancy another learn curve right now. Or at least that's the sensible answer, the real answer is that I have been working on that 1950s feel for the drawings, which I love so much, taking my lead from the likes of the L. H. Sparey book, among others – which I doubt I could get CAD to replicate (I could well be wrong on that).

Incidentally the typeface is Johnston Sans, which was designed in 1913 for London Underground and still used today. Again I live it and t's our house typeface, used on all sorts of work. Couple of examples here & here.

James

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