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Pete F
25th Jul 2016, 03:13 PM
I have a parting tool holder to suit insert tool holders, like this one. https://www.machineryhouse.com.au/L028

The issue with the above tool holder is that the holder for the parting tool blade then sits in an AXA tool holder, which goes in the QCTP ie it's a holder within a holder. The end result is it hangs out a long way from the toolpost and I noticed this was causing torque on the whole top slide when parting difficult materials.

I thought I could do better, so designed and made a tool holder that slides straight in to the QCTP and results in the parting thrust going straight down to the supporting way. I'll include a number of photos in case anyone wants to copy it. Everything is as compact as I dared to make it, with some overlap in features, and things like counterbores as thin as I dared to go. Function over form, and features are often asymmetric.

This the disassembled components. The dovetail is quite fussy to get exactly right. I cut one and it was fine, but it was toward the end of the travel of my QCTP handle. I preferred it to be toward the start of it so re-cut it. I could have left it, but was worried it may wear further as I use this holder a lot and it's not hardened. No biggie, I cut another, and the dovetail cutter I made the other week went through this steel like a hot knife through butter.

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This is the assembled unit. I didn't have many short 5 mm cap screws, and most of mine are longer. There's a very slight variation in head height as they're from different sources and I can see in the counterbores. I'll get some more (slightly longer) at some stage, but these are just fine for now.
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This is a close-up of the top part of the holder. The design is based on the original, but is a lot more compact. Also (hopefully) slightly less, well, crap than the original. The double bevels pull the blade in and down as the cap screws are tightened. That was also a bit fussy to get just right. All bevels are 45 degrees and I used a commercial cutter for them.

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Mounted in the QCTP

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The end result. This was parted at high speed (around 1500-2000 rpm) but that's faster than I'd normally use. I use cutting oil to lubricate the sides of the tool and it produces just too much smoke with a big cut like this and oil. I wanted to give it a hard time and see if I could crash it. I can't recall the type of steel, I know it's neither 1020 nor free turning, as both of them produce an excellent, almost mirror like, finish. It was a short I had in the scrap box and I just took the parted off piece and placed it on top.

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About the only other thing I can think of for anyone else making this, is the grub screw in these holders is M10 x 1. It makes sense to use a metric fine thread but I didn't notice and set up for a standard M10 (1.5 mm pitch). By shear coincidence I accidentally picked up a wrong tap and started tapping it as M10 x 1. I have marked that tap box now, as it's in the same series of manufacturer as all my standard taps, whereas my M10 is from another company. I thought something was wrong as the tap felt blunt. In fact the tapping drill size for that tap is 9.0 and not the 8.5 mm I used. As it turned out I can't seem to find any M10 x 1 grub screws that are long enough for this application, so I went back to standard M10. Lucky for me I realised early enough and there was no real harm done. Once the height is set and locked down it doesn't make any difference anyway. I used a straight knurl for the adjuster, as it should be for something that is turned only. A bit of turning etiquette there :wink:

All in all I'm very happy with the results and it's noticeably more rigid than the previous arrangement.

Edit: Unrelated, but I just noticed when reviewing the photos to see if they uploaded ok, that in the fourth photo you can see the thrust bearing I put under my QCTP nut. I thought it may help to reduce the friction when tightening the toolpost, and does indeed seem to make a marginal difference. I don't change my toolpost angle more often than I absolutely need to, but may eventually put a handle on this nut. We'll see. I thought the experiment was worth the price of admission for a cheap Chinese thrust bearing.

KBs PensNmore
25th Jul 2016, 08:58 PM
Now I know whats involved in making them. This might sound as a dumb question, but instead of trying to get the dovetail perfect, would it be possible to fit a sliding/floating gib that can be tightened/locked with a locking lever like this http://littlemachineshop.com/products/images/80/1477.80.jpg?

Kryn

Pete F
25th Jul 2016, 09:39 PM
The dovetail only needs to be perfect if you want to most rigid tool holder possible. What happens when the male dovetail is tightened is that it both expands and pulls the holder back toward to toolpost. The fussy part is to ensure the flat part that faces the QCTP tightens against the toolpost at the same time as the dovetail itself tightens, and both lock together at the same time. It needs to be accurate to within a few hundreds of a millimetre to get it just right. If you're not as fussy about it, you can have the dovetail only holding the tool holder, and that works just fine, but obviously won't be as rigid. It's why this wedge style of holder is more rigid than the piston style.

It's not difficult to do, just needs care. I took an existing holder I found was one of my better ones and copied the dimensions. First by getting the depth set to 9.50 mm (IIRC) and then measuring the distance between 10 mm pins. Once that was done just cut the dovetail until it matched. Always cheat where possible ;)

Pete F
2nd Aug 2016, 06:03 PM
Somebody asked what this finished up like, so here is the completed tool after (manganese) phosphating. The surface treatment isn't quite as even in colour as I'd like, but is functionally fine. I will try ultra-sonically cleaning before treating next time and see if I can get these finishes a bit more even.
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rcaffin
2nd Aug 2016, 09:18 PM
When you buy a QCTP set you usually get a parting tool holder very similar to what you have shown. Was there not one available? (Plenty of sets on eBay, although not cheap.)

Cheers
Roger

Pete F
2nd Aug 2016, 10:09 PM
The parting tool holders that are sold in those sets are nothing like what I made. They are intended to hold HSS parting blades and not parting insert holders. So I guess the answer is no, there was not one available.