Quick Change Parting Tool Holder

[wannabe]

Can anyone tell me the rake of the parting blade on a quick change parting tool holder.

I've bought a T type parting blade and I'm in the process of designing a parting tool holder for the QCTP but I'm not entirely sure how much rake, if any, to put on the blade. I've seen mention of 4 degrees and somewhere else mentioned 7 degrees so I'm wondering what the store bought ones are set at.

If possible could someone measure the angle on a store bought QCTP parting tool holder for me. Just the measurements so I can calc the angle would be fine.

[glenn k]

Not sure what the rake is the only angle I can measure on mine is 35 deg.

[.RC.]

AFAIK, it depends on the material you are cutting....It is the same rake as you use on all your cutting tools..

0° for brass
8°-10° for cast iron
10°-15° for mild steel
20°-25° for copper and aluminium

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[Greg Q]

My Aloris AXA style holder has the slot angled 4 degrees up. I haven't yet used it so cannot comment on its performance.

Greg

[Kody]

Well I'm diferent to all of you. I run my parting tool at zero to about 2 degrees of positive rake. At the moment it is zero degrees. My parting tool is about 2.5 mm wide or maybee 2,8mm wide. It is also made from HSS. I regularly part off 25mm dia mild steel at 250 rpm and 4320 at about 150rpm. The parting tool was ground from a piece of HSS only 1/2" square. What makes the tool work so fabulously is that it is mounted at the rear of the cross slide and upside down in its own toolpost. I would never use a parting tool in a "normal" tool post or a QCTP. The very best way is indeed to use it upside down. Until I get the tank and pump made, I spray the parting with WD40, it works a treat.

Kody

[wannabe]

My Aloris AXA style holder has the slot angled 4 degrees up.

I thought they didn't have much rake on them. As .RC. has said, in theory it should vary depending on the material you are parting however the QCTP type has to be at fixed angle which I guess is a compromise but 4° seems a little on the light side. I was thinking of setting it at around 7° - 10° as a compromise.
Can anyone comment on how good the QCTP type are or am I just wasting my time trying to make one and just stick with grinding HSS bits.

I snapped the tip off my 3/8" HSS parting tool when it bit in the other day and need to regrind it which takes ages to do so thought it was time to do the QCTP type with the T type parting blade but now I'm starting to have second thoughts.

Kody: I don't think it's possible to setup a rear mounted parting block on a hercus but I'll have a look at it. I've heard before that the rear mounted versions are by far the best solution.

[blackfrancis]

You can put a rear toolpost on the Hercus if you have what Hercus called an extended cross slide. I've always been able to part off from the front toolpost in my Hercus without suffering digins.

In one of his books, Geo Thomas shows why the rear toolpost works better with a nice diagram. When there is some flexing of the toolpost etc. the tool tends to disengage rather than dig in deeper as it does when mounted on the front.

There is a good way to achieve this with a front mounted toolpost. They used to sell parting tools with carbide tips brazed in that were mounted in a holder such that the blade is angled down at about 30 degs. These work really well but are on the large size for the little Hercus. You can make one yourself though. Take the HSS tapered parting blade blank you have. Instead of making a holder that orientates it such that it has 5 degs or so top rake mount it so it has 30 deg negative rake with the tool hanging an inch or more out of the holder. You then grind in the top rake at the end of the tool so that you have the appropriate rake at the tip. Make sure you grind the top rake back far enough that you still have clearance at the full depth you will be parting to. You won't believe how well these tools work until you try one.

Anyway I've put a very rough sketch down to give you an idea what the thing looks like.

[wannabe]

Anyway I've put a very rough sketch down to give you an idea what the thing looks like.

Ok. I can understand what you are saying. Just looking at I'd say it's going to have to sit fairly high up the toolholder, probably too high for the QCTP. I'll draw something up and see if I can get it to work in the QCTP or if not then some other form of holder.

[blackfrancis]

you are correct Peter, it will be high. Normally the holder is made from two pieces of steel, one that goes into the toolpost and the other that holds the parting blade. You can weld or bolt the two pieces together.

[Woodlee]

I have a QCTP rear tool post on the Myford S7 it works great .It has a HSS blade which is mounted upside down and set into the holder at about 4 degrees ,I just grind a shallow groove behind the cutting edge to make the swarf roll up into curls.
Ive always had trouble parting from the front , tried all the known remedies , speed feed coolant etc.The Myfords do suffer from lack of rigidty in the topslide because of the way they are mounted .


Kev