Hole shape when using a Seitz jewel-setting-tool reamer?

[Jon]

6 minutes ago, Endeavor said:

That's why I try to get to the source. Once the basic principle is understood, the rest is a logical consequence.

If the theory is correct, than Indeed, the amount of wobble will be the thickness of the shaving = amount of asymmetric.

The logical consequence would be that the to be reamed hole has to have the freedom to float by the amount of asymmetrically and can not be clamped fixed in relation to the reamer.

It's a bit difficult to explain in a non-native language, but I do hope that you get the drift of what I'm trying to explain

Makes total sense to me

7 hours ago, nickelsilver said:

It's much more convenient tapping the part in center with the spindle vertical.

 

 

That seems to be a lot easier

7 hours ago, nickelsilver said:

Here's some pics of my scope. It's a simple setup with a B8 shank that fits the tailstock. Ideally it would be adjustable in one axis, so the cross hair can be brought over to the hole edge, but as long as the hole fits the field of view it works.

What a lovely set up you've got there @nickelsilver

[Neverenoughwatches]

4 hours ago, Endeavor said:

Thanks for that John, now the have the Seitz side of the story, which corresponds with what already has been said.

I was trying to get my head around as to the why the reamer creates the movement, does my theory above makes any sense?

 

Ah so the holder doesn't attach to the tool its just hand held and the movement from the reamer is just an effect of that design of reamer. 

2 hours ago, Endeavor said:

That's why I try to get to the source. Once the basic principle is understood, the rest is a logical consequence.

If the theory is correct, than Indeed, the amount of wobble will be the thickness of the shaving = amount of asymmetric.

The logical consequence would be that the to be reamed hole has to have the freedom to float by the amount of asymmetrically and can not be clamped fixed in relation to the reamer.

It's a bit difficult to explain in a non-native language, but I do hope that you get the drift of what I'm trying to explain

I think i understand now Endeavor. Because the reamer has only one cutting edge the hole is growing in size  asymmetrically around its circumference. So the backside of the reamer has to occupy an increasing asymmetrical space. The amount of cut thickness it takes equals the amount of wobble. 

[Endeavor]

9 hours ago, Neverenoughwatches said:

So the backside of the reamer has to occupy an increasing asymmetrical space

Perhaps we are talking the same? In my virtual brain picture the asymmetrically doesn't increase, it is constant but shifting its position during the rotation, provided you ream with the same downwards pressure, i.e. the thickness of the shaving stays constant. In fact, the asymmetrically decrease towards the cylindrical part of the reamer, where the reamer tapers off.  The "problem" with this type of reamer is that the back-side of the reamer (the non-cutting) leans against the borehole whereas the cutting side digs in, enlarging the hole. One could see it a bit as following an increasing spiral predominantly in the horizontal plane.

 

9 hours ago, Neverenoughwatches said:

Ah so the holder doesn't attach to the tool its just hand held and the movement from the reamer is just an effect of that design of reamer. 

Correct. I do agree that there are nicer, perhaps better ways to enlarge a hole. Reaming with a one sided cutting action reamer seems crude, but, in the end of the day, if it works, it works.

I drool over Nickelsilvers machines, but those I may get in my next life

For now, and to me having solved the initial question, I can ream with these Seitz-reamers, when following the correct procedure, and be confident that I'll end up with a nice, in center and cylindrical hole.

Crude, cheap but effective.

I thank you all for your input ....... I think this was a thoroughly enjoyable and interesting discussion

Edited June 8, 2023 by Endeavor

[Neverenoughwatches]

5 hours ago, Endeavor said:

One could see it a bit as following an increasing spiral predominantly in the horizontal plane.

 

Thats exactly how i see it.  I meant the hole is increasing in size but not symmetrical, growing gradually as the cutter makes its way around the circumference of the hole. I think everything has been covered now haha

[Jon]

On 6/7/2023 at 12:51 PM, nickelsilver said:

Here's some pics of my scope. It's a simple setup with a B8 shank that fits the tailstock. Ideally it would be adjustable in one axis, so the cross hair can be brought over to the hole edge, but as long as the hole fits the field of view it works.

Beautiful set up there @nickelsilver. What do you use to grind such a fine boring bar, rather than buying them? I'm practicing honing some boring bars at the moment, but need a finer and better grinder

[Neverenoughwatches]

12 minutes ago, Jon said:

What do you use to grind such a fine boring bar, rather than buying them

Fine boring bar ? Is that the large chunk of hacked steel with the tiny cutting edge Jon ?

Edited June 10, 2023 by Neverenoughwatches

[nickelsilver]

6 hours ago, Neverenoughwatches said:

Fine boring bar ? Is that the large chunk of hacked steel with the tiny cutting edge Jon ?

It's a brazed carbide turning tool ground to bore very small holes. I think that one will do less than 0.80mm bores. In the hole is a plug gage showing the hole size.

6 hours ago, Jon said:

Beautiful set up there @nickelsilver. What do you use to grind such a fine boring bar, rather than buying them? I'm practicing honing some boring bars at the moment, but need a finer and better grinder

I use diamond grinding wheels. In my early days (like slightly pre-2000s) used a roughing wheel in a crappy WW lathe, then honed on a copper disc with 3 micron diamond paste. More recently, a proper grinding machine, with diamond wheels, rough and finish. All freehand,  and for tiny things like this, finish the functional faces on another (lathe object) with a really fine, D7, diamond wheel.

[Jon]

On 6/10/2023 at 1:45 PM, Neverenoughwatches said:

Fine boring bar ? Is that the large chunk of hacked steel with the tiny cutting edge Jon ?

Yes, that's it