Duplex Toolpost Grinder

This topic has 26 replies, 11 voices, and was last updated 16 December 2025 at 23:06 by Colin Heseltine.

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3 December 2025 at 17:35 #827515
Colin Heseltine
Participant
@colinheseltine48622
I have had a Dupex Toolpost Grinder for several years but never really needed to use it.

I now need to very slightly reduce the diameter of a hardened 90 degree seatcutter. I have made and fitted guards for the wheel and the belts, ordered a new belt but am struggling to find a source for suitable grinding wheels.

The wheels need to be 3″ diameter (or 75mm), 1/2″ thick and with a bore of 1/2″. I have managed to source some 1/4″ thick wheels but cannot find any 1/2″ thick.

A Midlands grinding wheel specialist can machine a 5″ one down to 3″ but will have a 2-3wk wait. Does anyone have any ideas on sources or even have a spare wheel they have no use for.

It is a Model D22A running at 1100rpm. Capacity is given as 3″ x 1/2″. Would I be correct in thinking that I could go smaller, say to 2″ diameter, safely.

Many Thanks,

Colin
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3 December 2025 at 17:57 #827559
noel shelley
Participant
@noelshelley55608
1100 RPM ? Do you mean 11,000 RPM ? As for size of wheel, smaller I would say yes but check the wheel speed rating ! It will reduce your cutting speed though this may not matter to much for a simple one off.

You do not name the supplier for the altered wheel but if it’s who I think it may be I had some 8″ wheels from them that were so far out of balance that they were unusable, only spending another £200 on a wheel balancer and a lot of work made these wheels any use. Good luck. Noel.
3 December 2025 at 18:29 #827564
Colin Heseltine
Participant
@colinheseltine48622
The motor states 1100rpm. Based on pulley diameters the spindle can run at 1500rpm max. Supplier was DGS Abrasives.

Colin
3 December 2025 at 18:41 #827567
bernard towers
Participant
@bernardtowers37738
Try abtec for wheels
3 December 2025 at 18:41 #827569
Bazyle
Participant
@bazyle
Does it have to be 3″? Die grinder wheels are smaller but more available.
3 December 2025 at 18:45 #827571
Diogenes
Participant
@diogenes
EDIT – overtaken by events –

1500 seems very slow for toolpost grinding?
3 December 2025 at 22:15 #827600
JohnF
Participant
@johnf59703
Colin, I have a small TP grinder, a Boxford Little Giant, no instructions but I do have instructions for a VERY similar Dunmore grinder — so similar I believe they may well be the same ? If you want the instructions message mw.

Looking for info on yours there’s some info on lathes.co.uk but no mention anywhere of your model D22A ! there’re others and as Noel says the speed you state is far lower than you will need for a 3″ wheel and more so for a 2″ wheel.

I purchased wheels of mine from Midland Abrasives

John
4 December 2025 at 09:53 #827623
noel shelley
Participant
@noelshelley55608
John has mentioned the company I dealt with. Are you sure it is a tool post grinder ? I would say that a 3″ wheel should run at 5000 +RPM. It is unlikely to cut properly at 1100 – 1500RPM. Noel.
4 December 2025 at 10:15 #827626
JasonB
Moderator
@jasonb
Any chance someone has swapped the motor pulley at some time. Looking at other similar ones the motor pully is much larger than the spindle one so would give a 6 or 10 times speed increase.
4 December 2025 at 10:18 #827628
Michael Gilligan
Participant
@michaelgilligan61133
On 3 December 2025 at 22:15 JohnF Said:

[…]

Looking for info on yours there’s some info on lathes.co.uk but no mention anywhere of your model D22A ! […]

https://store.lathes.co.uk/model/d22a

MichaelG.
4 December 2025 at 10:44 #827632
Colin Heseltine
Participant
@colinheseltine48622
The pictures below show the grinder mounted on lathe and also the motor plate.

Currently no guards or belt fitted.
4 December 2025 at 11:12 #827635
noel shelley
Participant
@noelshelley55608
The speeds mentioned put me in the mind it is NOT a grinder ? Those speeds are more appropriate to a milling attachment. Or the pulleys have been changed ? Noel.
4 December 2025 at 11:23 #827637
Colin Heseltine
Participant
@colinheseltine48622
Lathes.co.uk under toolpost grinders have a Duplex D22A listed and have manuals, but not seen any pictures to check on pulley sizes.
4 December 2025 at 12:08 #827642
Michael Gilligan
Participant
@michaelgilligan61133
Can’t see that exact model here:

https://www.lathes.co.uk/duplex-toolpost-grinders/

But it certainly looks like there was a wide range of wheel sizes

MichaelG.
4 December 2025 at 12:29 #827644
Colin Heseltine
Participant
@colinheseltine48622
Im beginning to think the motor pulley has been changed to a much smaller one. Am going to look at a manual I have located and see how much the wheel has to be scaled up to get the recommended speed.
4 December 2025 at 17:47 #827662
onion
Participant
@onion
Colin, with regard to a source of grindsrones may I suggest that Black and Decker used to sell a 3×1/2×1/2 grindstone for use on a drill chuck arbour back in 60’s. There are 2 on an auction site at the moment (one very expensive, the other given as metric size) I have looked for my virtually unused example for you to try but haven’t found its hiding place. I’m sure other forum members may have better luck. The auction pictures of the items suggest around 5000 max rpm

Neil
4 December 2025 at 19:00 #827683
JohnF
Participant
@johnf59703
On 4 December 2025 at 10:18 Michael Gilligan Said:

On 3 December 2025 at 22:15 JohnF Said:

[…]

Looking for info on yours there’s some info on lathes.co.uk but no mention anywhere of your model D22A ! […]

https://store.lathes.co.uk/model/d22a

MichaelG.

Thank you Michael, I didn’t look in the store only the main archive here — https://www.lathes.co.uk/duplex-toolpost-grinders/#google_vignette

John
4 December 2025 at 19:18 #827687
Clive Brown 1
Participant
@clivebrown1
On 3 December 2025 at 18:29 Colin Heseltine Said:

The motor states 1100rpm. Based on pulley diameters the spindle can run at 1500rpm max. Supplier was DGS Abrasives.

Colin

If, as should be on a grinder, the motor is a fixed speed induction motor, then 1100rpm seems a strange speed for 50hz. Is it possibly a 6 pole motor intended for 60hz. Definitely too slow as it stands.
4 December 2025 at 19:41 #827691
noel shelley
Participant
@noelshelley55608
It appears to be a brushed motor, note the brush holders. I have a wolf tpg and it is also a brushed motor. Angle grinders and small high speed grinders seem to be brushed. Noel.
5 December 2025 at 08:35 #827732
Clive Brown 1
Participant
@clivebrown1
You’re correct, I’d not noticed the brush-holders.
5 December 2025 at 19:44 #827842
Kiwi Bloke
Participant
@kiwibloke62605
For what it’s worth, this late in the thread, here’s some info. from an old Duplex brochure. Sorry, obviously no help with wheel availability …

Model D22A.

Plain wheels: Ext. 3″ X 1/2″ X 1/2″; Int. 1″ X 1/2″ X 5/16″ (‘standard vitrified’)

Motor: Universal (DC or SP, commutator-type), 1/3 HP

Speeds: 6,000, 16,000 RPM

Unfortunately, the brochure pics don’t show the belt pulleys, but there doesn’t seem enough room in the belt guard for a large enough motor pulley to give the speed ratio required if the OP’s stated motor speed is correct.

Later production models were fitted with fully enclosed induction motors. The commutator motors were not intended for continuous use, but their duty cycle was not stated. Spindle bearings are oil-mist lubricated – a few drops of oil required ‘every few working hours’.
10 December 2025 at 12:00 #828307
Colin Heseltine
Participant
@colinheseltine48622
Kiwibloke,

Thanks for that speed info. Currently waiting for a manual and some brochures. Looks as though I need to make new motor pulley. Need to do some calculations to work out the diameter. I will keep the spindle pulley as is.

Should have a suitable stone and belt to drive in current form by end of week. Hopefully this will enable me to do the current job as its only a case of reducing a diameter, finish is not critical.

Colin
11 December 2025 at 05:33 #828352
Kiwi Bloke
Participant
@kiwibloke62605
Colin, I just dug out my ancient, but little-used, Duplex D 27 (C). It is old enough to have a universal motor, like yours. There’s no motor plate per se, just a plate on the belt cover giving spindle speeds (6,000 & 16,000 RPM) and motor power (1/3 HP). A rough measurement of the heavily-crowned flat belt pulleys and a couple of sums gives the motor speed as between 10,000 and 11,500 RPM (approx.). It certainly screams… Probably not a good idea to run the motor unloaded!
11 December 2025 at 09:51 #828371
noel shelley
Participant
@noelshelley55608
The figures given by Kiwi are inline with what I fancy some, including me would expect. The speed rather than being 1100RPM is probably X10, this would make sense. A ratio of 1: .55 or 1: 1.45 . Noel.
16 December 2025 at 17:15 #828988
Colin Heseltine
Participant
@colinheseltine48622
I have now collected the new 3″ dia grinding wheel and the new belt. I have also purchased one of the cheap digital laser rpm counters.

Initial check of the motor gave speed of 15633 at the motor pulley. This gave something like 26000 high speed for use with an internal grinding spindle and 7144 for the low speed for external grinding. Ideally I need to take a number of speed readings and average them out.

I could possibly accept that whoever stamped the motor plate missed a zero off and it should read 11000, in which case this would give a low speed of 6490 and a top speed of 15155 with the current pulleys.

At least it looks as though I have suitable speeds for the size of grinding wheels I will be using.

Cheers all.

Colin
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