It's Stuart Hammer time......

[Sanjay F]

I appear to have a wall not a curve??

[Jasonb]

If the blued corner was vertical then you have come down too far.

In no particular order I touch off on the red to get sideways position and zero handwheel or DRO. Then move away so I can touch down on the blue position and again zero wheel/dro. then move up and away

Move to the end of the work then return to your two zero positions and make the cut.

[Sanjay F]

Yeah suspected I'd over done it somewhere.......glad I'm on a test piece! 

I took a file to one of the edges I'd just incorrectly milled and it came out looking fine & dandy, but not repeatable I guess. Let me have another go tomorrow

I'm wondering which to make first, the piston rod or the holes in the mouthpiece, which is easier to modify 

EDIT When you say make the cut, is this more than 1 cut, several smaller passes?

[crueby]

In the pics, it looks like the height started  out okay then it  went lower? Maybe thats just camera angle, if not then either the bar was not level to the table, or the bit slipped in the chuck. Are you using a end mill holder with side set screw? Holding in a drill chuck is a bad idea, the bit will move on you.  And I  would  make a number of light passes, moving in or down a bit at a time depending on  which is your 'fixed' axis.

[Jasonb]

At that size one pass should not be a problem.

[Sanjay F]

In the pics, it looks like the height started  out okay then it  went lower? Maybe thats just camera angle, if not then either the bar was not level to the table, or the bit slipped in the chuck. Are you using a end mill holder with side set screw? Holding in a drill chuck is a bad idea, the bit will move on you.  And I  would  make a number of light passes, moving in or down a bit at a time depending on  which is your 'fixed' axis.

I think its the camera angle as I deliberately trammed the milled before I started today. The cutter is held in an ER32 collet and arbor of the correct size.

I think a bit more practice is required and do you have to do any filing/rubbing down after or does the milling give the necessary edge

[crueby]

At that size one pass should not be a problem.

Depending on quality of cutter, rigidity of machine, quality of holder, yes. Several passes allows for sneaking up on the position/depth, it can be tricky to get them right in one go. Lots of ways to do it.

[Dave Otto]

The way Jason pointed out is the way that I have always done it. I will usually back off each touch-off by one or two thou. then zero out the DRO, Keeps from having a line on your work-piece if you don't hit your zero spot on. But yes, depending on the size of the radius usually always take multiple passes. It is basically a form tool and they don't like heavy cuts.

Dave
 

[Chipswitheverything]

Re. which to make first, the mouthpiece or the rod, I think I'd probably do the shaped holes in the m'piece and gland first, get them as accurate in size and position as possible, and then aim to do the fitting on the rod.
 The holes need to be nicely aligned in concentricity with the bore of the cylinder, so if that has been got right by careful machining, it might be better not to wander away from that attainment by doing much in the way of subsequent filing of the holes.  The rod will be easier to take down to a sliding fit and a nice finish by light draw filing along its length.

[Sanjay F]

Re. which to make first, the mouthpiece or the rod, I think I'd probably do the shaped holes in the m'piece and gland first, get them as accurate in size and position as possible, and then aim to do the fitting on the rod.
 The holes need to be nicely aligned in concentricity with the bore of the cylinder, so if that has been got right by careful machining, it might be better not to wander away from that attainment by doing much in the way of subsequent filing of the holes.  The rod will be easier to take down to a sliding fit and a nice finish by light draw filing along its length.

Thanks Dave, I was leaning that way, but good to confirm 

[Sanjay F]

After a few test cuts things are improving, going a little bit too far in horizontally, but vertically looks good (see corner top right)

I'm going to make another test piece, round off the edges and then can look at making the slots in The Bush and Gland (is that the name of a pub?  )

[crueby]

A bigger radius cutter, and you can make your own round bar!   




Always fun to learn a new tool...

[Sanjay F]

A bigger radius cutter, and you can make your own round bar!   

Always fun to learn a new tool...

Well I think I've made the test piece as good as it's going to get, I did use some emery on it to get the finish and a slight line out, but it's good enough to use as a gauge.

Yes, new tools & skills, the face mill is new to me and I finally have the finish I've been hoping for over the last couple of years and now the rounding cutter .............that's what's great being a late comer to this hobby, all this stuff to buy and justify to the wife! 

[crueby]

Looks like you've got  it!

[Chipswitheverything]

I like Chris, Crueby's suggestion that a big rounding cutter could be used to make square bar into a piece of round bar ...!!  I've got a few larger external rounding cutters, next time I'm stuck for a bit of 6mm bar I think that I will definitely try that out!

It did occur to me, though I haven't really thought it through, that to get the best concentricity between the shaped gland/ ,well fitting, we hope, piston rod, and the bore of the actual cylinder above the mouthpiece and gland, so that the piston is sliding nicely, there is a set up that might be tried.

That is, that the turned spigot to fit the piston onto, on the top of the hammer rod, is left for the time being, until these other components have been made.  Then , the square section of the hammer shaft is held in the four jaw chuck ready for the piston spigot, -  and the m'piece / gland slipped over it, and the internal bore of the mouthpiece clocked true.  ( Note which flat of the hammer shaft is at the back , and mark it so that the orientation is kept that way ..)
By doing this, the piston location can be kept true to the cylinder bore, even if the gland and m'piece guidance have not turned out to be absolutely concentric with the cylinder bore.