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.

[Author]

Posts