Low speed grinder or standard for lathe tools?

[Russ BParticipant @russb]

I'm looking at taking the plunge on a decent (new) grinder. I'm looking at 8 inch grinders and wondered if I should get

a low speed (1425rpm) which is slightly cheaper and has 32mm wide 60g grey and 120g White aluminium oxide wheels.

A normal (2900rpm) 40mm wide 36 and 60 carborundum wheels (possibly Norton)

 

I like the idea of low speed – I'm sure the grinder I used at Sheffield Hallam was a low speed grinder and it seemed quiet and easy to use. However the wider 40mm wheels sound like a nice thing to have – especially if they're Norton Abrasive wheels but I haven't confirmed that yet.

I could possibly pay a little extra and get the slow speed grinder with 40mm Norton wheels if they fit?

Edited By Russ B on 30/03/2016 10:52:02

[Russ BParticipant @russb]

[Jon GibbsParticipant @jongibbs59756]

Hi Russ,

I have a slow speed grinder and find the extra "thinking time" very useful for freehand grinding. I'm not sure the slower speed makes that much difference for jig-based grinding though really.

I do use white AlOx wheels in preference to grey carborundum wheels though, although my grinder gets used for other tools than just metalworking.

HTH

Jon

[Ady1Participant @ady1]

I always assumed that a grinder needed to be "high speed" ie circa 3000 rpm

…You learn something new everyday

[Russ BParticipant @russb]

I have confirmed the 40mm wide wheels are indeed Norton Abrasives (made in china) as standard but the grinder comes with 36 and 60 grit, which is possibly to coarse for lathe tooling, can anyone advise?

I'm struggling to get consistent information searching online.

The cheaper low speed grinder comes with 60g grey and a 120g white AlOx for finishing

I'm tempted to go for the slightly cheaper low speed unit and gamble that the finer unbranded 60g/120g wheels are any use.

It is a £150 grinder so it's hopefully a far cry from my £20 B&Q brand which ended up costing me more in decent grinding wheels!

Edited By Russ B on 30/03/2016 12:09:09

[egaParticipant @ega]

I am no expert but the wheel manufacturer will know the correct peripheral speed for his product ie the speed at which it cuts most effectively and therefore does not tempt the user to press too hard.

The slow speed (dry) grinders are marketed as suitable for woodturners.

[DustyParticipant @dusty]

As ega points out slow speed grinders are basically for woodworking tools. Grinding HSS lathe tools is a far cry from wood turners chisels and gouges. 36 and 60 grits are not to coarse, they are the grits I have on my grinder and work very well. As you have not advised us on what grinders you are looking at it is very difficult to give sound advice. If slow speed grinders were the best option then many thousands of engineering workshops would have them installed, they do not. The most important consideration is that the grinder has sufficient power, it is no good starting to grind a tool when the grinder slows to a stop, due to lack of oomph.

[MWParticipant @mw27036]

Like someone earlier said, on a jig a slower speed wouldn't be needed but for sharpening tools by hand a slower speed could help with the control over the finish. I do find that it is hard to accurately control this by hand at high speed. I personally know someone who grinds drills by hand by holding the grinding wheel in a pillar drill, which obviously is much slower than what most grinders go up to. More speed just means faster removal rate and more heat as a result, if you look at some much older tool grinders they are slower, you couldn't attempt this with a normal grinder because it would stall under load. 

Michael W

Edited By Michael Walters on 30/03/2016 15:48:12

[AjohnwParticipant @ajohnw51620]

8" and 3000 rpm as it's usually stated is a good size for grinding HSS lathe tools with the correct grade of wheels. It's not just grit but the make up of the wheels as well. 10" is often used in toolrooms I have been near. There is usually a feeling about that bigger is better all down to surface speed.

I wish I could help on grade of wheel but from buying from the usual sources i can't say as I am very happy with them. As some people were using 6" wheels and I wanted another grinder I bought one and fitted it with the white wheels Axminster sell. They are passable. I think the do 8" too,

My grinder in the dirty area was bought a long time ago. Green grit on one end for carbide and a grey 60 on the other end. Finish mostly depends on how quickly and evenly the tool is fed across the wheel. There is a catch though. This grinder doesn't need bolting down as it doesn't shake about and the wheels needed very little dressing from new. Hardly any at all actually.

If anyone can remember the tool room grades that were used I for one would be grateful. There were 2 one assumed lathe tools were not reground too often and had a very long life. The other grade broke down more easily so didn't need dressing very often. Both by Norton and grey and both in real terms lasted a long time.

John

–

[DustyParticipant @dusty]

I have to take issue with your statement Michael. Finish has not so much to do with the speed of the wheel more the size of grit in it. Yes a grinder running at 3000rpm is going to have the ability to remove metal faster, it does not mean it has to, heat should not be a problem with HSS, it just makes the tool difficult to hold, if it is overheating then you are using to fine a grit. Keeping the wheel dressed is just as important to prevent overheating and for achieving a good finish. A fine hand stone to just finish off the tool is the usual trick. Tool grinding is an art learned over time there are no quick fixes, I should know I started in engineering in 1959.

Edited By Dusty on 30/03/2016 16:45:20

[Russ BParticipant @russb]

The grinder is an Axminster Engineers Series 8". It weights in at just over 28kg so its a big lump. The Grinding wheels are over 1.6" wide (200mm x 40mm with a 32 bore)

The motor is "only" 550w which is quite a lot to be fair, however some smaller grinders quote much larger figures, probably startup or near stalled, I don't know to much about motors.

[Russ BParticipant @russb]

The other low speed unit was an Axminster trade series 900w which had thinner 32mm wide wheels (still more than comfortable) but much finer grades (60 and a white ALOx 120).

It also has an LED light which is neither here there nor there, I have a 2ft flurecent directly (30cm!) above my current grinder)

Thanks for all the opinions and shared experiances so far. I'm leaning towards the full speed "Engineers Series" unit with those Norton Wheels which is what pulled me in in the first place – It also benefits from an extended 3 year warranty which is nice, although I wouldn't expect it to last any less than 10 given its rare use!

I've added a pair of new slip stones too – I dropped both of mine over winter and they obliterated – I've been working with the left overs which are actually quite handy, I used my diamond hone to reshape them. I've got some hand scraping to do on my Myford mill column riser so I need a good fresh flat stone.

[John ReeseParticipant @johnreese12848]

When run at lower speeds wheels behave as if they are a softer grade than when run at high speed.

[mechman48Participant @mechman48]

Just make sure whatever machine you use that, 'the spindle speed should never exceed the wheel speed'

George.

[DustyParticipant @dusty]

Looks like a useful bit of kit. You will need to make some sort of dressing attachment to keep the face of the wheel flat with a wheel of that width. Umps and ollers in the face of the wheel will not help you.

[Russ BParticipant @russb]

Grinder received today – but damaged sadly!

Strangely no damage to the large wooden crate it came in. I must admit, I'd underestimated the size of this thing….

The left wheel has several dings out of it. It is a (Chinese) Norton Abrasives wheel – Axminster had arranged a replacement and collection of the old wheel within 30 seconds of calling them so I can't complain about that. The left side guard and rest are also out of shape – I can't see any missing paint or marks so I don't know what's going on. I've had a look at the grinding rest and it looks like it was lined up by eye and all 4 or so pieces welded in about 15 seconds – typical Chinese quality and care…. but that doesn't explain why the circular guarding is all of out square. Any how, one of the Aftersales team are going to give me a call back about that one to see if they have a whole replacement guard. It sounds like they may have to exchange the whole thing – I better fish that wooden crate out of the Biffa bin at work!

I'll highlight the good/bad bits for now and reserve judgement on the left side.

It has a nice soft start (a bit too nice maybe… it takes a while)

The grinding rests are quite firm but one of the 3 end plate screws goes through the grinding rest slotted hole stopping it from tilting to grind angles! The securing bolt for the rest is also near the back, so you can feel flex.

Inside the inside half of the guard there is a small half nut that has just one tiny spot of weld, as the screw pulls though, the nut has lifted and is skewed now making it a bit hard to get the screw in and out.

The big plastic thumb/wingnuts on the spark guards are very nice to use and the guards feel secure – they don't get in the way.

The 40mm wheels have a recessed hole as the shafts only look long enough for 25 maybe 30mm, the front and back machined washers that clamp on to the paper ring are very substantial and very nice quality, they look like cast alloyed tool steel, kind of like a modern carbide insert type boring bar. The centre adaptor is also a very nice sliding fit.

The wheels don't run true, the end face is all over on them both, unlike the English made 6" Norton Wheels I have which ran perfectly true right out of the box, I squared them up just for the sake of it when I fitted them.

The paint on the right rest has been touched and it sticks out like a sore thumb (it'll soon wear off)

One of the rivets on the right spark guard has been pulled as the gun was being removed to do the next, so the rivet isn't seated, and it leans off at an angle.

The quality of the right hand guard and the rest, is good and it feels pretty strong, I just wish they'd have taken double the time to weld the rest up and triple the time for the left side! A whole 30 seconds to do it in, and maybe a simple jig would have gone a long way!

Overall, I'm reserving judgement till I know what's happening with the major issues but in general, I think it's pretty safe to say, it's been thrown together – as usual with a lot of these cheap things, it really needs assembling properly (including probably going as far as cutting and regrinding the rests together but I'll wait till its out of warranty before I cut it up!)

As far as Axminster goes, they seem to be very much on the ball, its just a bit of shame they didn't catch this before it went out the door!!!

[Russ BParticipant @russb]

Well, that was a bit of a saga but all sorted now.

After some inspection and much messing for a few days after delivery, I was unable to get the rest on the left wheel aligned to the (albeit damaged) grinding wheel. The mounting flange was bent and was unequally popping in and out and pushing the rest between toe in and toe out, making it impossible to align the dam thing to the face of the wheel.

I received a replacement grinding wheel after about a week as promised by customer services. I didn't know what was happening with the bent guard as they just said they'd passed it to another department (The Technical Team)

A few days after the wheel, I received a perspex eye guard, not a wheel guard, so I got back in touch, and an apology was made, and again, I was left in the dark while the technical team looked in to it, a dispatched email landed in my email box, so I knew things were in motion.

I then received a full wheel guard, for a 150mm grinder……. another email to customer services, but this time no response at all (embarrased? annoyed at me?).

A few days later another dispatch notification landed and finally after 3 weeks, I have a replacement 200mm guard!

I will fit the guard and wheel tonight with a bit of luck.

SO, eventually, we've got what I ordered albeit still with a few imperfections on the right hand grinding rest and left side eye shield rivets but it is a tool not an ornament so I can live with that, so long as the wheel isn't damaged and the guard and rest are doing their job I'm happy enough.

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