Just a bit of nomenclature – "rod" is generally understood to be of round cross-section, so "flat rod" is a contradiction in terms. I think you mean strip or bar?

What you need are PARALLELS which are a standard item used in milling and many other operations. Ideally they are ground flat and parallel. You can buy sets, but they would probably be too wide for a vice on the vertical slide. You can actually often use a bit of ground rod such as silver steel but getting a bit the right size could be tricky. Alternatively buy some bits of thin (say 3mm) MS strip which could be sufficiently accurate of various widths – and you could mill them down to make a set covering the various dimensions you need. IIRC Harold Hall describes making parallels on his website? It is good practice to tap the work down against the parallel AFTER tightening the jaws. In the vice it shouldn't be possible to move the packing when the jaws are tight.

If you use a packing piece behind the work in the chuck as you describe, if the jaws are properly tight it should be possible to tap it out using a small hammer and a drift to help make sure the force is in the right direction not to shift the work.

Further to Johns post steel parallels are commonly 1/4" or more thick which makes holding thin components difficult without supplementary packing. Thinner ones can be found down to 1/8" or so thick but these are quite tricky to use as the tend to tilt. You should use the thinnest parallel that can be fitted commensurate with leaving enough msterisl above the jaws to machine.

For thinner parts normal practice is to use spring (wavy) parallels which are spring steel strips made with several waves along their length. Typically around 1/2" wide across the waves so the stand up nice and stable. When the vice is done up the waves splay out allowing the parallels to compress until the part resting on them is gripped.

As John says normal practice is to beat the part down when the vice is quite tight to ensure that it is properly seated on the parallels. Generally tightening and beating needs to be done in stages with typical home shop equipment due to accuracy limitations allowing tiny movement during the tightening process. Considerable restraint is needed when beating on thin parallels. When more on way ones as these are easily damaged.

Beating down is an acquired skill. You need a resilient striker to avoid bounce back.Historically a lead hammer was the historical weapon of choice for the professionals. The vice jaws need to be both smooth and quite tight so the part slides down and stays down. Firm hitting, hammering a nail style, is frustratingly unproductive. I use a 16 oz, nylon faced, Thor dead blow hammer held loosely and strike with a flicking motion so the haft bounces gently in my hand on strike. All the work ins don by the momentum of the head. Usually works.

Larger parts are best done with two parallels. Theoretically you should be able to get the part firmly seated on both but in practice the accuracy of affordable vices and the component being worked on is rarely good enough to get both dead tight. The slightly loose one ensures the job hasn't tilted so its still important.

Clive

Edited By Clive Foster on 22/06/2021 10:14:16

For setting work in the 4-jaw chuck I use aluminium extrusions/gauge plate/HSS toolbits as packing if the work needs to be set away from the chuck body. I never leave the packing in place when turning. Friction is not sufficient to keep it in place with any certainty even if the work is tapped into contact.

For spacing work in the machine vice I use piles of gauge plate or accurate (better than I can measure) parallels made by the late father of a friend, who was a toolmaker. If I don't need to remove the packing I will tap the work down. If the parallels need to be removed (for thru drilling for instance) I don't tap down. The lift on the vice is small anyway.

Andrew

Some make bespoke spacers for their chuck – such that the ‘spider’ is retained by the chuck jaws.

I would not bother with the vice as it can introduce more errors than needed.

Set the vertical slide up with a dit to get the table parallel with the lathe axis. Put a tee nut in the middle slot and screw a stud into that. Slip cylinder over stud and with a bar or heavy "washer" and nut clamp cylinder with true face against table.

You can now machine the port face by raising/lowering the vert slide to get the cutter stepover, carriage to set depth of cut and cross slide to move the job back and forth to actually make the cut. Only cross slide should be unlocked.

Also keep "slot drills" for slots or plunge cuts, a sharp 4 flute cutter would be best for this say 1/4" stepping over 3/16" per pass.

EDIT, something like this

Edited By JasonB on 23/06/2021 10:27:52

Have a look at the last page or two of the twin Victoria thread. if you don't know which end is true true to the bore then turn up an arbor to mount the cylinder on and turn the end(s) true on that as suggested by Ramon. You then have flat faces to ref the port face to.

As Above, mount on an arbor and skim the end on the lathe

Here

That looks OK

If you have not already seen it then DocG's earlier thread on his 10V is worth a read even if it was done with a mill as well as the lathe.