PDA

View Full Version : Roughing gouge problem



Tiger
15th October 2005, 08:22 AM
Dear all,

I am using the set of chisels that comes with the Hare & Forbes 900 b/w centres lathe. I am having a real problem with the roughing gouge. All other tools will sharpen nicely and respond to some sort of honing but not the roughing gouge provided. I can not ever get it super sharp from the grinder and any attempt at honing seems to dull the tool fast. I have been turning a lot of redgum and the roughing gouge is not cutting all that well. I have tried different angles from 35 to 50 but no real improvement. If we assume that I haven't destroyed the temper of the blade (which wouldn't be easy because it's a fair bit of steel), why am I having this problem? The tool is high speed steel. Any advice appreciated.

JDarvall
15th October 2005, 09:29 AM
I'm new to lathe work, Tiger. But I have been grinding chisels for some time. I'm not having any problems grinding this gouge. The ones that I find tricky are those fingernail spindle gouges.

Is your grinder dressed properly ? ....can burn high speed steel, but that grinding wheel would have to badly underdressed for that to happen, I reakon. Should be able to get it sharp enough straight from grinder. Keep your finger up close to the edge while you grind to monitor heat. But first, I'd dress that grinder. definetly

goodluck

Utuk_Xul
15th October 2005, 12:42 PM
Roughing gouges work best with a burr on the edge. Make sure your stone is well dressed and do not hone the roughing gouge. Leave the burr on.

Tiger
15th October 2005, 02:35 PM
At first I thought it was the grey wheel. So I dressed that. It made little difference. I then put a 40 grit white wheel on the grinder. It too made little difference. Dressed it and still no difference.

Only thing I can think of is that the redgum is so severe that it is playing havoc with the gouge. Maybe I'll have to take special steps with Redgum in future.

Captain Chaos
15th October 2005, 06:55 PM
G,day Tiger,
When sharpening high speed steel it is recommended that a white ( aluminium oxide ) grinding wheel be used, around No. 80 grit seems to be the general consensus. Too much finer & the tool cutting edge overheats when grinding.:eek: I use a No.120 grit wheel when sharpening but for different reasons. I just have to be a bit more careful monitoring heat build up at the tool tip.
It almost sounds if your roughing gouge is not the same grade of steel as your other gouges, i.e too soft. When you next grind your bowl gouge, take note of the colour of the sparks as you grind. If the steel is the same as the rest of your tools the sparks should be the same colour as those from your spindle / bowl gouge or what ever. I've been informed from a reputable source that if the steel is of a good quality / hardness that the sparks should be a very red / orange colour.
Redgum, and several other Australian timbers are very unforgiving on tool cutting edges due to high silicate content in the timber ( wood, lumber, stuff? ) Blunt tools has been a time honoured tradition since the first fleet lobbed onto Aussie shores.;):D
The only other suggestion that I might make is to purchase a name brand roughing gouge, e.g. Sorby, Crown, Hamlet or our own P&N brand.
Take good care,
Barry. ( CC )

Skew ChiDAMN!!
15th October 2005, 07:31 PM
I turn a lot of regdgum and it does play havoc with my chisels... except it blunts all of 'em about equally fast. I do have a seperate roughing gouge I use mainly on harder woods though and keep it sharpened @ 60°-65° which helps it hold an edge longer.

Just to clarify: the 60°-65° is the angle between the cutting face and the axis of the tool. (see link to pic)

http://www.woodworkforums.ubeaut.com.au/attachment.php?attachmentid=11391

I have seen this same angle referred to as 25°-30° elsewhere... which can lead to confusion and producing an edge that's too thin and friable. The reason for the less acute angle is it leaves more steel behind the cutting edge, which helps dissipate heat better as well as making it less prone to blunting/chipping. When the edge starts to blunt during a session I can usually simply retouch it up with a diamond lap maybe four or five times before I need to take it back to the wheel. This also helps extend the life of the tool. :)

BTW, don't use the grey wheel... [shudder] That overheats the metal, if you see the very cutting edge of the tool (less than a mm!) turning blue you know that it's too hot and if it is just carbon-steel you have ruined it's temper and will need to regrind until past that section. :( HSS is more forgiving, but it's still not a good idea to grind until you blue the tip. A lot of light grinds with pauses for cooling in-between is much better than one heavy "go-for-broke" pass.

Stick with the 60-100grit AlOxide (white) and just put a new bevel on the cutting edge. With each sharpen the bevel'll grow larger until it's all one face again. Why waste steel when just changing the angle and not actually reshaping? ;)

As has been said, leave the burr on. IMHO it doesn't improve the cut any but it doesn't detract either and it just ain't worth the effort to remove.

Mike Jefferys.
16th October 2005, 05:59 PM
I had a similar hassle with a P&N 40mm roughing gouge which is the forged pattern (stamped out of a length of flat bar) not the milled patterns which are milled from a billet of solid HSS. The reason, I discovered, was the roughness in the flute. It's again a heads up for P&N, they must run a mill down the flute of this otherwise magnificent tool as a final stage of manufacture and not just belt it into a more or less gouge shape and leave it at that with an un-milled and unpolished flute. Any edge tool ideally has to have TWO equally polished and sharp surfaces which meet at the business edge, the angle is frankly a secondarry issue although critical for other reasons I agree. Ask yourself how sharp a piece of broken glass is with an angle of probably 90 degrees.
I fixed the problem by honing the flute with several grades of fine Wet & Dry and the tool is remarkably improved. It can be futher improved - maybe with a mop and compound?
Finally don't assume that a set of tools are either made equal or from the same manufacturer or the same steel etc etc.
In my humble opinion there is no call for burrs on cutting tools and burrs are for scrapers only. Burrs on cutting tools mask the lack of and edge and give the illusion of being sharp. If you want proof of this take the time to hone a skew on a Japanes water stone using say a #1000 and #600 grit hone. The result is astounding - it's just that turners usually are not or can not be that fussy.

Skew ChiDAMN!!
16th October 2005, 07:34 PM
Mike's right about the flute although, IMHO, it's a secondary issue, as is the burr. If the tool won't seem to take an edge I'd be inclined to blame one or the other but if it's sharpeneing OK and blunting rapidly, well... I'll stand by what I said.


In my humble opinion there is no call for burrs on cutting tools and burrs are for scrapers only. Burrs on cutting tools mask the lack of and edge and give the illusion of being sharp. If you want proof of this take the time to hone a skew on a Japanes water stone using say a #1000 and #600 grit hone. The result is astounding - it's just that turners usually are not or can not be that fussy.

Not wanting to start yet another sharpening bun-fight... but I have to add that this depends on what the tool's being used for.

With a roughing gouge, especially on redgum, you can spend 10mins putting an edge on it that'd circumcise any gnats flying past but in less time on the wood it loses that extra li'l bit of sharpness; then it's no better than if you'd left the burr on. Then it won't last any longer before needing retouching.

I just don't see any sense in wasting time removing the burr in this case! But I guess it's a case of whether you belong to the "technical theory" or the "buggrit, let's get the job done" school of thought. :D I guess that those who turn out "works of art" have different priorities to production turners. C'est la vie. [shrug]

When you're making finishing cuts, not roughing, then the edge makes all the difference in practise as well as theory. After all, it only takes a couple of passes to clean up and the extra edge should last longer than that. :)

Tiger
16th October 2005, 09:59 PM
Thanks for the advice fellas. I now suspect that it is the dastardly redgum which has affected the roughing gouge. I tried some huon pine and the gouge worked a lot better but not quite as good as it once did. I generally put a hone on skew chisels and parting tools and they slice the redgum nicely leaving a terrific finish. The roughing gouge, however does not respond to diamond honing or slipstone or anything I have tried making it terribly frustrating as I always use the roughing gouge to start spindle turning. I lose so much time going back and forth to the grinder and then having to try and cut with a dull blade.

Some of the replies have mentioned a white wheel of 60, 80 or 100. I bought a 40 grit wheel, I've noticed that the finish is slightly serrated, what is the optimal wheel to buy in terms of grit? I have only ever used the 40 grit grey wheel but I learnt a long time ago that you have to have a very light touch, but I've been disappointed with the 40 grit white wheel (which is what I was advised to buy).

Mike Jefferys.
16th October 2005, 10:23 PM
When the tools from unknown manufacturers become branded and preferably have a hardness testing dimple then we'll be able to be more certain because we will have a bit more to go on (although this can be faked easily!). The point about the roughing gouge is well made - it is a roughing tool so no point really in stuffing about with a superfine edge which will be knocked about in a few minutes anyway. Personally I only hone the skew, for two reasons, it's easy to do and it's the finishing tool used with greatest finesse so it benefits from the few seconds it takes. On balance I'd say you have a dud tool. Do the other tools in the set blunten as fast on the same wood? There may be your answer.

Mike

Skew ChiDAMN!!
17th October 2005, 01:18 AM
When all else fails... buy another tool! :D

One other thing that may make some difference; the presentation of the tool. Most people I've watched tend to introduce the gouge square on to the tool-rest, so the cut is always at the bottom of the flute. Personally I angle it left or right a bit (depending on which direction I'm making the pass) so the cut is moved to the left or right wing, introducing a "slicing factor." ie. It's almost cutting like a skew chisel instead of a parting tool, if you follow what I mean? :confused: Also, as one part of the cutting edge bluntens I tend to roll the gouge so that it's cutting on a fresher section of the edge.

Both mean I have to change the angle of attack to get bevel rub but I'm guessing that should be second nature to you by now, you sound like a practiced turner. ;)

Neither will fix your problem, but they do increase the practical working time between sharpens. [shrug]

rsser
17th October 2005, 09:39 AM
Hi Tiger,

I wouldn't worry about the grit too much, esp. with a roughing gouge. Some would argue that the wheel's friability is more critical than its grit.

Redgum varies a fair amount in its density and if it's not blunting your other tools at the same rate I'd be suspecting the steel quality.

As for the flute issue, Sorby polish it three times on their tools. P&N typically have rough flutes on their big gouges and Mike's right in saying the turner has to fix this. In my case regular slipstoning along the flute improves the edge.