Parting Clearance

Dunno where you got that from

regards Mark Rand RTFM

?? Generally the blade top is horizontal ??

I've found HSS parting blades come in three types - flat topped, step-topped, and w-topped.

I think the w-top is deliberate, and is meant to make the chips curl into the center; the flat top is - well, normal; and the step-top looks like an artifact of cheap manufacture, though it may be that way for a reason - anyone?

I usually grind the step-tops flat, then leave them alone - otherwise I never touch the tops, only grind the end.

then the cutting edge becomes narrower than the shank

ohh, don't grind the sides. Just make sure the blade is exactly parallel to the motion of the cross slide..

A load of interesting comments however I have some comments with regard to HSS type part off. This post is general but relates to some of the comments made

1 The top of the HSS blade is usually not flat due to the method of clamping. Therefore it must be ground flat before use. 2 If the blade is held horizontal then cutting rake needs to be ground. 3 Once cutting rake has been ground any touching up on the front requires that the top be ground down to match the height 4 If the blade is held at a rake angle then touch up on the front is all that is needed. 5 Either option of tool holder means that if a different rake is required say between brass or aluminium then really a different tool bit is required. The grinding discussed above therefore needs to be repeated. The Horizontal holder is therefore best suited for brass the angled holder I assume gives more grind problems for brass.

All of the above means that the newcomer to machining (and possibly many old hands) has major problems dealing with parting off.

A last point - the concept of "grooving" an inch deep with no side clearance to the tool makes little sense to me.

I appreciate that this type of parting off with HSS has been with us for a long time, but there is now a MUCH better way. If the OP had used an insert blade then I am sure this thread would never have started

Richard

Thanks to all for the interesting comments on grinding HSS blades, this was one of my original concerns - I have lined up the blade as accurately as I can and I still get a concave cut - I'm wondering about grinding the side of the tool to get more clearance - though I also have an idea for aligning the tool accurately. Interstingly once the part is parted off the tool starts to cut the convex end left in the chuck - I find that very peculiar as it seems to me to suggest that the blade is being pulled to one side rather than pushed off line.

I'm still interested in pictures of home made tipped holders - unfortunately I wasn't able to view Mark's pictures.

I looked at the Sparey, Duplex and GHT designs before I made the toolpost. I rejected the Sparey design because I thought the mounting to the cross slide was too small in area and used only a single bolt. The lathe is a Boxford and other Boxford users had commented on rear toolposts being in the way so I wanted to hang the toolpost off the back of the crossslide - both Duplex and GHT have variant designs for that purpose - originally intended for the Drummond. I decided that as I was making a separate base for the post a separate turret would add another joint without much gain. I didn't like the GHT mounting for parting blades because I don't want to use a 1/16 blade with a 1" overhang - I've tried this and I can see the blade deflecting. I was however keen to try and present the blade to the work in the way GHT descibes so I decided to make a separate toolholder to hold the blade - it uses GHT's method of adjusting the vertical position of the blade with grubscrews in the tool holder. I also reasoned that a separate tool holder would give me more flexibility if I wanted to change to carbide parting tools. There is an indexing pin in the base at the back left - similar to GHTs but shorter and so probably less accurate.

The only design I looked at during construction was GHT's.

Russell

Russell, I have been making 2 replacement 18T 20DP gears from the gearbox on a Myford Super 7 ie without a lead screw. The work is being carried back and forward between the lathe and the Warco MillDrill and the gears ganged on a bit of 1" bar. Consequently, I have had to both part off and recess with the GHT tool. I used a new Eclipse blade which had only been corrcectly ground at the front but had NOT been vee'd. The lubricant was lard oil which had collected foolish wasps over several summers. I had no problems although the lathe is past its best- and is repairing itself.

Having said all that, I would love to know how you ground and sharpened your blade. It sounds a bit like 'flaming' but what do you use to inspect your finished blade? I use a watchmaker's loup but have a traditional microscope and a cheap children's one. Again, I use a waterproof felt tip to check that I have ground away the worn part of all my lathe tools- and then hone so that I can see my dirty finger nails reflected in the work.

Apart from my poor efforts at cleanliness, GHT and Martin Cleeve both went along similar lines.

GHT said- there are no hairs so fine that cannot be split

Cheers

Norman

Hi Norman, To determine a sharp edge, you first have realize what constitutes a sharp edge. Sharp, ignoring grind angles, means the arris between two flat planes. In simple terms this means two flat surfaces meeting with no rounding of the meeting point. Any rounding blunts the edge, and the simple way to see this rounding is to look in good light, a blunt edge will reflect light, a sharp one will not reflect any light.

Comments anyone? ned Ludd ===

My dear old Dad was renowned for his tool-sharpening skills. One of his favourite sayings was, "Look at the edge in good light. If you can see it, it isn't there!"

Just as you are saying.

JW² ===

Ned, But I don't have a problem! I have a Clarkson. It's bit of a rattle trap. I made a Quorn- a bit rusty like me. I have a Kennet for weekdays and bought for curiousity and 'shirt buttons' at fabricated smaller Stent. With the help of a more computer literate than I, I made 113 pages of grinding information onto those in MyMyford Group.

I was toddling around the blacksmith's shop in 1933 and I was fiddling about with a friend's watchmaker's lathe in 1941.

Sorry, at 78+, but one gets rather 'Deja vu'

Norm

I think I heard that before. :) Ned Ludd

(lots snipped)

Hi Norman

My tool grinding technique is quite simple - I've not been doing this long enough to find a complicated way. For the parting blade I clamped a straight edge to the side so that I could see how I was presenting it to the wheel. I used the side of the wheel (which I generally try and avoid) to finish the top surface of the blade and ground the front on the front of the wheel finishing with a vertical pass to get the grinding perpendicular to the edge. I didn't inspect the edge too closely but relied on making sure that my grinding reached the cutting edge on both faces. I honed it lightly - no corner radii.

When I mounted it in the lathe I used a straight edge on the top of the tool to try and see how well the top surface was aligned to the lathe axis. It looked OK - within the limits of how well I could see the gap between straight edge and cutting edge.

My latest plan is to turn a bar parallel so that I can use a square to check the alignment of the tool but I've been distracted by playing with the Adept shaper I just bought.

Russell

Shades of 'Baissez-moi et la'- yep, I do speak French. Russell, You now have a little Adept shaper- and very nice too! You can now make nice little jigs, perhaps out of ally so that you keep your biceps down to reasonable size. You now can make the little holders that George Thomas suggested in MEWM( yes?) You could make the 140degree front vee far more simply and accurately than before. If you do, you will find that it will not wander so much as a straight cut blade. With a carefully made holder to hold your parting blade, you could do the 140 degree top or a curved one using a drill press. I'm not sure that I could hold a Dremel steady enough! A baby jig would ensure that using a flat surface that your work would be parallel. After all, for a 2" cut you only need to 'vee' an inch.( sounds like I am trying to teach you to suck eggs, but I am definitely not)

Presently, I'd love to have half an hour with your baby Adept. You don't live in Geordieland, I suppose?

Let me know how you progress

Norman

If I can't cut 4" steel stock in under 5 minutes the blade is shagged.

John S.

And John,

I gave the idea of such things as a snotty nosed little kid out of the gutters of the dirty biggest open sewer in the World in----1944. I sold spinach from the garden and bought myself an education.

I came in from my few pennorth at the local flea pit where the film was the old mining film of 'The Stars look down' and an old wrecked man was in the tin bath and my mother was bathing the cuts that started from the old man's buttocks and went up and up his body as the greasy wire rope had cut and cut almost through to the bone. The cuts stopped thankfully before they severed his neck. That Old Man was my father- Old Bill, the colliery blacksmith. A few years later, I had moved on a bit. My father had been trapped with a colliery loco tube that he had been fitting. Happily, the hospital had found 'something else' but in the next beds in the Royal Victoria Infirmary in Newcastle four miners laying dying with their guts riddled after a misfire with coal and slate.

I must have looked at sight when I got back to the office but dear old Hicky took me under his wing- and the rest is -well, history.

Tomorrow night, I'll get the same nice invite to put on my best dinner suit and climb the stairs- and look at Hicky's name in bronze with the rest of the Masters. I've been offered the Master's Chair many times. Of course, I cannot fill his chair with the same wisdom.

One thing that he taught me was there was more things in life than cutting a 4" billet of steel- not in 5 minutes but in my whole lifetime.

Norman

[]

If I can't cut 4" steel stock in under 5 minutes the blade is shagged.

John S.

Hi John, would that we had your equipment, experience and 4" stock to play with :>) Ned Ludd

Do threats work on parting tools then?

Mark Rand RTFM

Hi Norman

Looks like it's back to the library for me then. I'd wondered about the grooved tools but haven't experimented (yet).

I lived in Geordieland in the early 80s for a while but am now in rural Derbyshire.

The Adept looks like it should be useful - I have a Tom Senior hand shaper too - but I don't have space to leave it set up and it's so heavy that I'm always reluctant to get it out. That shouldn't be a problem with the Adept!

Russell

On or around Sun, 22 Feb 2009 14:27:56 -0800 (PST), ravensworth2674 enlightened us thusly:

I've got that book of that, it's good. As is "The Citadel".

Russell, I'll happily bung in a useful heap of bumph if you e-mail me at snipped-for-privacy@n-atkinson.wanadoo.co.uk.

You could make the GHT whole thing but alter it a tad for the Boxford. The clamping idea could be done easily on the shaper( uh huh?)

Cheers Norman

In article , Mark Rand writes

Ouch! Scary place in my mind now, Mark.

David