What parting off tool and how to get parallel faces?

[interferencefitParticipant @interferencefit]

Hi all,

I’m gradually learning my way around my Myford 7. I’ve been doing a few small jobs, sometimes learning the hard way!

Today’s project was making a 15mm thick aluminium spacer to fit a new CBN abrasive wheel to my bench grinder. I started with some aluminium round bar, bored the centre hole to a nice snug fit, and then turned the outside diameter and the end face. Since I don’t own a parting tool yet, I clamped the bar in a vice and cut the spacer off with a hacksaw.

This is where things got tricky. I needed to face the rough, sawn side, but I found it incredibly difficult to chamber the short part back into the chuck so that it ran perfectly parallel. I only discovered how off it was after mounting my new wheel on the grinder and noticing some obvious run-out, which I traced back to the non-parallel faces of the spacer.

I did try a few ways to square it up in the chuck. First, I tried using a centering tool in the tailstock, but the part was too short for that to be accurate. Then, I tried passing a piece of square stock through the chuck jaws to push the part flat against, but it was far too hit-and-miss. The experienced machinists among you are probably face-palming right now, which is exactly why I’m here for some guidance!

I fully appreciate that parting off the piece would have prevented this issue entirely. This brings me to my first question: What parting tool should I buy?

My lathe has the original Myford quick-clamp lever system (with the spring-loaded black block).

 

AI  suggested a blade-style holder However, I also saw this traditional-style tool on the Myford website I am not sure how the blade style works with my specific tool post, whereas the second one looks like my standard tools (though the blade doesn’t look very deep).

Which style would you recommend for my setup?

My second question is about technique: How do you accurately face the second side of a short, bored workpiece? If you have to flip a short part in the chuck to finish the opposite face, what is the best method to ensure the two faces stay perfectly parallel and true to the bore?

Thanks in advance for any help!

 

 

[Andrew TinsleyParticipant @andrewtinsley63637]

I always move the saddle up to the chuck and adjust the parting off blade against the flat of the chuck face. This way you cannot get the parting off blade to be other than at right angles to the lathe axis.

Of the two parting off tools that you show, the one with replaceable blades is best. However you will need to make an adapter to hold it in the traditional Myford tool holder. Unless anyone else has a smarter idea.

Andrew.

[JasonBModerator @jasonb]

To save us repeating a lot of things have a look at this post from earlier in the week

 

Parting off

regarding facing thin parts, a set of soft jaws are the ideal thing for this. You machine a shallow recess in the jaws the same diameter as your part and the back of the cut gives you something to push the good true face against.

[bernard towersParticipant @bernardtowers37738]

If no soft jaws slide a piece of parallel steel through the jaws and push your spacer up to it, remove spacer and face off. An old bearing would make a good spacer but that would have to be left in place. Alternatively use a V tool to machine a vee in the work beyond your finished length, cut off then fit in chuck and use the v line to set true. There are so many ways to skin a cat!!

[HollowpointParticipant @hollowpoint]

Another method for facing thin washers, gears and other objects is to super glue the part to a faceplate or any flat surface. (Could just be a large bit of faced off bar). This is a common method used in watchmaking, though shellac was more traditional. Heat it up with a blowlamp to break the glue bond.

As for parting tools, I like the carbide insert type with the “U” shaped grooved tips. Get the thinest one you can. 1-2mm ideally.

[KEITH BEAUMONTParticipant @keithbeaumont45476]

one trick I use is to use  the small moly magnets on  the jaws to pack out for holding thin parts  near the chuck

[Howard LewisParticipant @howardlewis46836]

The HSS blade will probably last far longer than a brazed carbide tip (I seem to be able to chip them rematkably quickly.

In contrast to the HSS tapered blade that i was given when buying a “pre loved” ML7 some 40 years ago, used on its successor, and still not worn out.

With regard to holding, I would suggest turning up a holder (Collet), on the 3 jaw, with a recess to hold the washer, if soft jaws are not available.

The rear face of the “collet” will be square to the lathe axis, and the machined front face of the washer will seat against this, so that the hand sawn face can be faced parallel to the machined face.

HTH

Howard

[egaParticipant @ega]

If you are sticking to the Myford “clog heel” tool holder then you might consider getting their tools mounted in a “boat” with an arcuate slot which gives height adjustment. The standard set included a parting tool.

When/if you upgrade, I wouldn’t rush to get a quick change holder. There are numerous designs for height adjustable holders which will serve you well while you decide how to go in future.

[Clive Brown 1Participant @clivebrown1]

Another way for the OP to solve his original problem is to use a back-stop in the lathe mandrel. Hemingway/Reeves market a kit specifically for the Myford 7. Making one is likely to be an interesting exercise. https://www.hemingwaykits.com/HK2010

[Howard Lewis]

On Howard Lewis Said:

The HSS blade will probably last far longer than a brazed carbide tip (I seem to be able to chip them rematkably quickly.

 

HTH

Howard

the cheap far east one’s chip very easily, the industrial standard one will last you forever, but the price i

[Howard LewisParticipant @howardlewis46836]

When I had the ML7, the standard Myford tool clamp was replaced by a Myford four way tool post.

Boat holders make height adjustment easy, but alter the rake angle as the cutting edge is adjusted.

Although many consider it a faff, I prefer to shim the tools to centre height. (Am not a lover of big top rake angles. The rear toolpost mounted HSS parting tool has zero rake, and very rarely causes problems)

Reputedly, QCTPs are a little less rigid that a four way, and not a lot quicker changing tools, unless there are a lot to do.

With four ways, front and rear, that causes me little problem, most of the time.

Usually only knurling or radius turning call for tool changes.

But you must optimise your set up.

Howard

[egaParticipant @ega]

Howard Lewis:

Might you post a photo of your rear four way?

[FulmenParticipant @fulmen]

It’s not too hard to make a chuck spacer for these jobs:

https://www.homemadetools.net/forum/attachments/machinist-chuck-work-spacer-019.jpg-2079d1413923321

 

A simpler one would be to weld three flat pieces of steel to a bolt like a Y.

[Chris CrewParticipant @chriscrew66644]

Some people confuse brazed finishing tools with parting tools which should be no more than about 2mm wide at the tip. Any tool wider than this is likely to be a finishing tool, intended to ‘rub’ the ‘thread’ off a longitudinally turned piece. A bit like setting a knife tool askew to rub to produce a finer finish. I seem to recall GHT or Sparey  had something to say about this.

[egaParticipant @ega]

IIRC, GHT “set tool almost to rub”.

[bernard towers]

On bernard towers Said:

….

 

 

An old bearing would make a good spacer but that would have to be left in place…

Make sure the bearing is big enough that it won’t come out between the chuck jaws, or it could be flung across the workshop when you start the lathe. Or take it out first of course.

I would have guessed the steps on the chuck jaws of a myford were less than 15mm, so just use the outside jaws

 

[old martParticipant @oldmart]

For a beginner, the RDG blade and holder is much superior, and easy to keep sharp and on centre height. There are lots of printed plastic spacers to fit in chuck jaws on the market, you do need to find out if there are any to suit your chuck. Soft jaws are very good for holding difficult work and even when worn down can be drilled and tapped to hold new home made tops. With your chuck you would need to know the exact dimensions of the jaws including the “actual” pitch of the teeth before chancing buying soft jaws.

[Howard LewisParticipant @howardlewis46836]

ega

The  article about its construction was published in MEW 306, August 2021 and MEW 307, September 2021.

It wan’t for the Myford, but a little larger, for my Engineers Tool Toom BL12-24 (Warco BH600 / Chester Craftsman etc lookalike), to look as much alike to the fronmt toolpost.

It required no mods to the lathe itself, the base being bolted to the Cross Slide.

So with different dimensions, or modifications, could be made for any lathe with Tee slots on the Cross Slide.

It was made by laminating pieces from a 1 metre length of ground 3″ x1″ that I’d been given.

Each of the laminations was machined differently from the others.

The graphics team made a good job of tidying up my drawings of the G A and parts.

If you want any extra help, just send me a message with your E mail address, and I do my best

Howard

[egaParticipant @ega]

Howard:

Thank you. I will turn up the MEW articles and bear in mind your kind offer.

[old martParticipant @oldmart]

Another quick fix to get anything short running square, assuming the right side is already flat and not simply saw cut is to bring the tailstock up and use the end of the chuck with the jaws retracted to hold the work against.

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