Designs for a 1/2″ hacksaw blade type parting off tool holder

[GreensandsParticipant @greensands]

Hi all – I have been experimenting with using conventional 1/2"W x 0.025"Thk hacksaw blades for use as a parting off tool with the principal aim of being able to put in a narrow run-out/undercut in various brass steam fittings currently under construction. Problem is finding a design of tool holder suitable for holding a hacksaw blade given that the one I use for the standard Eclipse type parting off blade is not really suitable for the job. Can anyone recommend any more suitable designs for the holder?

[GreensandsParticipant @greensands]

[peak4Participant @peak4]

You seem to have a Myford sized lathe, but not sure what toolpost.
I have something similar to this one from Chronos, but mine, rather than a wedge, holds the blade with an angled flat plate, but the same broad principal
https://www.chronos.ltd.uk/product/spare-parting-blade-holder-myford-quick-change-toolpost/

Note that it's intended for the slightly wedge shaped HSS parting blades, so holds my hacksaw blade at a slight angle from the vertical, but since I'm only using it for shallow grooves, it's never been a problem. I leave the blade in the holder when re-sharpening.

If you were to make one from scratch, just milling the slot with a dovetail cutter on the bottom edge, would leave a vertical face for the blade to butt against.

Bill

[GreensandsParticipant @greensands]

Hi Bill – Yes, it is the Chronos unit (or one very much like it) I have tried using to hold an hacksaw blade but the blade is not a comfortable fit and I was hoping for something better.

[Ramon WilsonParticipant @ramonwilson3]

I made one for doing some deep fins on a cylinder head. I don't have any dimensions to hand but this is what it looked like. The blade was clamped by small cap head screws, the holder then held in a Dickson Quick Change Tool Holder as normal

It's quite a while back but I think I hand ground the end of a slot drill to give the slight angle (dovetail) on both lips which worked well enough to give a good grip on the blade.

Hope that's of help

Tug

[Nigel Taylor 2Participant @nigeltaylor2]

My design for this. Slot in bar was cut with slitting saw. Set in teeth of hacksaw blade removed with careful use of a hammer.

[Clive Brown 1Participant @clivebrown1]

Here's my home made holder. Made from 1" x 1/8" and 1" x 3/16" BMS held together by 4 x 4 BA csk. skt. head screws.

The blade sits across the 2 lower screws. I use it a lot for small stuff including steel.

It will easily part 1/2" dia. brass.Sharpened in seconds of course.

[bernard towersParticipant @bernardtowers37738]

I think one of the things to remember is use a all hard hss blade, most people use bimetal blades in their hacksaw frames (too flexible for this job). plus one for Tugs system of holding the blade in place. I also make them from machine blades which are HSS.

[JasonBModerator @jasonb]

Must admit that for the purpose of undercuts that the OP wants to do I've taken to using a DCMT or DCGT insert to do both the initial turning and then the undercut which saves having to change tools and also gives a nice rounded fillet to the root of the undercut which should be a lot stronger than a square cut one.

.

[peak4Participant @peak4]

This is my Dickson style one.
It came in a job lot, so I've no idea of the manufacturer; I've never seen one like it before or since.
It doesn't seem particularly high quality, as the mating surfaces to the toolpost itself haven't been ground, but it works well enough.
There was a similar one in the batch, but for a deeper carbide insert/blade type parting tool; It has a deeper step at the bottom to drop the tool tip height appropriately.

Bill

[Clive HartlandParticipant @clivehartland94829]

Having worked on Swiss instruments I noticed that the did not do undercuts on shafts, but did recess facing galleries. These better to retain any lubricant' To my mind an undercut gives a weak point on the shaft at the junction of main body!

[GreensandsParticipant @greensands]

Many thanks to all who have responded to my request for some design detail. I am now in the process of making up my own version based upon the ideas shown here.

[duncan webster 1Participant @duncanwebster1]

Posted by Clive Hartland on 25/07/2022 22:25:57:

Having worked on Swiss instruments I noticed that the did not do undercuts on shafts, but did recess facing galleries. These better to retain any lubricant' To my mind an undercut gives a weak point on the shaft at the junction of main body!

Not if you only undercut to the root diameter and have a radius on the left corner of the tool (looking from the top).

[GeoffTParticipant @geofft]

What a good idea. After reading this I have made my version. As someone who struggles with wider parting tools I found this easy to use. Think I will alter it to change the screws to countersunk heads to get closer to the chuck jaws. Sorry if the picture is wrong way round.

GeoffT

Edited By JasonB on 01/08/2022 19:07:37

[DMBParticipant @dmb]

Clive and Geoff's 4 screw clamp type for old hacksaw blades. I am certain that type appeared in one of the older traditional books on model engineering but unfortunately I cannot remember which one. It could be as far back as a "Duplex" book. Not tried making one but I think the design shows promise of effective Ness. Probably won't bother making one unless a special need arises as I'm very happy with my RDG Tools version. The HSS blade has been sharpened both ends in opposite directions so it could be switched, with it's holder, from front to rear toolposts without repositioning the blade. Looking forward to completing machining the rear toolpost to try.

John

[Roderick JenkinsParticipant @roderickjenkins93242]

Posted by DMB on 01/08/2022 19:28:42:

Clive and Geoff's 4 screw clamp type for old hacksaw blades. I am certain that type appeared in one of the older traditional books on model engineering..

John

It's a Len Mason design from "Using the small lathe". Here's mine:

Very useful for small E clip grooves.

Rod

[Nigel Graham 2Participant @nigelgraham2]

A point to bear in mind – I have found this by trying it – a plain saw blade with the teeth ground off is likely to jam not very far into a deep cut because it has no side clearance. Even more so if not absolutely perpendicular both vertically and horizontally to the axis.

It may best to leave the teeth on, and arrange them at the top, so they shave the walls of the kerf a little (just as they did when they were part of a saw.) Obviously creating a top rake, needed only at the cutting edge, will remove the first one or perhaps two, teeth but that should not be a problem.

Arranging the blade teeth-down is of course very likely to create a swarf-trap, also jamming the tool.

[HopperParticipant @hopper]

Posted by Greensands on 25/07/2022 15:53:06:

Hi all – I have been experimenting with using conventional 1/2"W x 0.025"Thk hacksaw blades for use as a parting off tool with the principal aim of being able to put in a narrow run-out/undercut in various brass steam fittings currently under construction.

For doing a relatively shallow undercut like that, you would be as well off to grind your own grooving/parting tool from a piece of 1/4" square HSS. You can then put side clearance on it so it does not jam.

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