Relief grinding

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Warpa
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Relief grinding

Ive just had a quick read of what it is, but is it needed. Everything i read seems to have conflicting replies. When i get my cylinder and bottom blade ground i should back lap it, i then get told that if it was done properly it should not need it. Now im reading after grinding it should be relief ground.

I want to get this right on my 1st mowers but am unsure what i should be looking for and how best to preserve the cylinder and bottom blade over the years. I just read on this website that grinding is a last resort and back lapping is fine and what Ransomes suggest. If that were the case it would mean i can finish my 2 mowera as the grinding cost is holding me back.

wristpin
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Extensively covered on this

Extensively covered on this forum many times!!

Warpa
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Well it appears relief

Well it appears relief grinding is not for the Ajax ackording to the company grinding my cylinders, its too thin and Ransomes have already done a backlap to thin the blade.

hortimech
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I would suggest you find a

I would suggest you find a different company, an Ajax cylinder blade is unlikely to be thinner than a John Deere greens mower cylinder blade and JD mandates relief grinding. Also the Ajax blades are not 'backlapped', they are just 'scalloped' to make them thinner near the actual cutting edge.

There are very few cutting cylinders that cannot be relief ground, in fact the only one that comes to mind is the old Toro 1000 single greens mower and that is only because its cylinder was only 3 1/2 inch diameter approx 

Edda
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I have a few old Certes hand

I have a few old Certes hand mowers and I would only grind/relief grind if the blade edges were damaged. Back lapping should be enough to put an edge back onto the blades so that they can cut paper when checking for sharpness.

My own personal choice if I had to re-grind would be to use the relief grinding method  this means the only the tip of the cutting edge is touching the bottom blade at any time.

hortimech
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Sorry, but backlapping can

Sorry, but backlapping can only maintain an edge, if the 'edge' has gone, you will never get it back by lapping the cylinder.

Also, if you spin grind a cylinder correctly, you get a similar result to relief grinding, the problem is, a lot of people do not spin grind correctly, they allow the cylinder to spin out until there are no sparks, this is wrong.

wristpin
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My own personal choice if I

My own personal choice if I had to re-grind would be to use the relief grinding method  this means the only the tip of the cutting edge is touching the bottom blade at any time.

Not just correct cylinder grinding for a good cut. A little back relief on the top edge / lip of the bottom blade , and a 5 degree back angle on the front edge * both help.

*  Different manufacturers recommend different angles.

 

Warpa
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Also, if you spin grind a

Also, if you spin grind a cylinder correctly, you get a similar result to relief grinding, the problem is, a lot of people do not spin grind correctly, they allow the cylinder to spin out until there are no sparks, this is wrong.

You said i should find a different place to grind my cylinder but here you say if its spun ground correctly you get a similar result to relief grinding.
Whats to say they dont spin grind correctly?
He did explain why they do what they do and how different things make a difference, more so on industrial equipement where how things are sharpened can save a lot of horsepower and fuel. He also went on to explain how it affects noise etc and most of it went over my head, but i gathered he knew his stuff and was also well into the vintage mowers. They have a Greens zephyr and Ransomes ripper that that they use on the lawns there as well as one of those robotic mowers.

hortimech
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You posted:

You posted:

Well it appears relief grinding is not for the Ajax ackording to the company grinding my cylinders, its too thin and Ransomes have already done a backlap to thin the blade.

I take it this came from the company and it is wrong, you can relief grind an Ajax cutting cylinder (I should know, I have done a few in my time). As for Ransomes thinning the cylinder blades, I take it this refers to the back edge of the spirals being thinner than the root, this is fairly standard and has nothing to do with relief grinding or backlapping.

As I said, John Deere mandate relief grinding of their Greens mower cylinders and they have similar spirals as the Ajax. It also doesn't matter wether you are grinding a recent cylinder or a vintage one, the same rules apply.

 

Warpa
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This quoting is confusing

This quoting is confusing things. You said spin grinding correctly gives similar results to relief grinding. You also said to find a proper company that can relief grind.

I said what is to say this company does not spin grind correctly and therefore relief grinding is not required.

 

This would for me then raise the question for me cutting 60m2 lawn would i ever need to back lap once all is sharpened. It should take a few seasons untill the blades start to dull.

hortimech
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You basically said that your

You basically said that your Ajax cylinder could not be relief ground because of what your 'company' said. I based my comments on that, if your 'company' says that an Ajax cylinder cannot be relief ground, then, to me, it sounds like they do not know what they are talking about,as you can relief grind an Ajax cylinder. I know because I have relief ground Ajax cylinders, I have even relief ground Suffolk Super Colt cylinders.

As for spin grinding, this can give results very similar to relief grinding, but only if it is carried out correctly.

Backlapping is a maintenance procedure and needs to be carried out on a 'sharp' cutter unit to maintain the cutting edges. If any of the cutting edges are dulled or damaged, you cannot repair them by backlapping.

If it is of any help, can I point out that I spent over 40 years in the lawnmower trade, serving my time as an apprentice engineer and I hold the parks and gardens city & guilds.

Warpa
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I dont doubt anything you say

I dont doubt anything you say and City and Guilds is the only qualification i recognise as a carpenter. This new fast track NVQ qualification serves no purpose.
While i have no idea on cylinder grinding i do know old school trades are always right. My way is the only way, but others will argue their case.
Now while i dont know the specifics of a 60 year old grinder or a super modern one i do lnow there are more than one way to skin a cat.

While i will maintain all day long an electric planer is the best way to remove 3mm off the top of a door, the next generation argue that a plunge saw is superior. I lnow its not the same but it does explain the angle i look at things.

The Ransomes intrustions say to backlap and came with the tools to do it, if my blades are not relief ground does that mean back lapping cant be done, or will just use more paste? If we were discussing carpentry tools there are different ways that achieve the same results, i sharpen my chisels by grinding a concave onto the edge so when i finish on a stone the surface being ground is a lot smaller and therefore quicker. Im in my 50s and got taught by men older than i am now. The way i do things can be frowned upon because they know no better.

To conclude i have no idea if you are right or wrong and unless you were chatting to the old boy doing my blades no one is right or wrong. When i collect the cylinders i will bring this up and pay more attention to what he says.

Thank you for the input as i like to understand how things work and why they work that way.

Edda
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I have 3 Ransomes Certes push

I have 3 Ransomes Certes push lawn mowers all fitted with new cylinders made at Garfitts. One of the cylinders was manufactured wrong the overall diameter was too big. To remove surplus material from the cylinder I had to get it relief ground (My choice), and I will only back lap if it starts losing its edge (will not cut paper when adjusted).
The other two cylinders from Garfitts were spin ground I think and again I will back lap only when they lose their edge, although I only use the two 14 inch versions nowadays not the 16 inch.
Going back to your question if you did get them ground in my opinion their is no need to back lap.

hortimech
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If you wait until the

If you wait until the cylinder has started to loose its edge, then you have waited too long. Backlapping is a maintenance procedure, little and often. You cannot sharpen a cylinder by backlapping, you can only maintain a sharp edge.

wristpin
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Interesting about your

Interesting about your oversize Garfitts cylinder. I had the same problem a year ago with a new cylinder for a local cricket club’s Auto  Certes.  Also had two bottom blades for Mk VII Punches which should be lipped but were supplied flat. They maintained that they should be flat - until I pointed out that their own on line catalogue said lipped ! However, they did replace them with the correct ones.

wristpin
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As many of us are confined to

As many of us are confined to barracks with time on our hands , this may make interesting reading. Particularly from around page 34 onwards.

https://cdn2.toro.com/en/-/media/Files/Toro/Commercial/education-technic...