Thread: Hercus 9" parallel turning accuracy

If the .002" taper is not effecting what you do then yes its ok.
I prefer if there is a taper for the job to be larger at the chuck.
.002" over 80mm is a fair bit.
Most of the Hercus lathes that I have set up are around the .0005"/.001" on a work piece 150mm from chuck unsupported.
I try for a nearer result when setting between centres over 200/300mm sometimes achieving sometimes not depending on the day.

Thanks pipeclay,
So just keep shimming it up at the front of the tailstock? Or is there some practical limit that suggests you look at something else?

Cheers,
Matt.

I dont use the methods you mention when I test lathes ,I intially make sure they are level/flat on there base 1st.

Hi Matt,
I need to do this with my 260, so I'm interested in the discussion. I wonder whether having only 20mm of the bar held in the chuck is enough? Did you do it that way for a reason or were you limited by the length of bar you had?

I've attached a copy of the South Bend 10K accuracy report. It shows the tolerances SB allow for a range of lathe measurements. The test you are performing is at the bottom of the page. They allow a maximum of 0.0003" (0.0076mm) difference between the two collars. Unfortunately they don't specify the distance between the collars. I'm sure that figure is out there on the web somewhere.

Hope this helps.

Chris

Hi Chris,
Thanks for the Southbend test report. In lieu of anything else, these seem like good guidelines to apply to the 9".

The Hercus Textbook of Turning suggests 3.5" between collars, if my memory serves me correctly (haven't got it in front of this PC but I assume you've got the Textbook).

I only had 20mm in the chuck as per the instructions in "Lathework". Also this bit of bar (being dia 30mm) that I was willing to turn into swarf obviously won't go in the spindle bore of a 9", so I just stuck with Harold Hall's instructions - 20mm in the chuck and 100ish hanging out.

I haven't got a machinists level and I haven't found any low-tech ways to level the lathe (not that I've really looked yet) so I'll persist with shimming the tailstock until I get a better result.

Where are you Chris? If you aren't far from Albion (3020) then perhaps we can swap notes on our lathes?

Cheers,
Matt.

Matt,
Thanks I have the ToT. You're right it says 3.5" between the collars.

I don't have a machinist's level either. I tried a levelling method known as "rolly's dad's method" to level my lathe bed. However, until I turn up some test collars I can't be sure if it was successful.

I'm in mt Eliza (3930).

Matt I am pretty much a novice at this. But I think it's important to have your lathe stand as level as you can get it . If your floor is uneven, it makes a marked difference to your finished tolerence. My lathe was turning a taper , something like 2 thou over a short distance, very bad. I levelled the base, did nothing else, and the difference it made is amazing . In my case, the floor slopes both ways, down and across, this was twisting the whole stand . Mike . PS All I have is a builders level but the bubble was showing a distinct lean in two ways.

I am yet to follow why you are shimming the tailstock when you said you turned the bar unsupported?

The taper you have shown is not consistent... That to me tells me either your cut was done wrong or something is severly worn...

I would guess that your cut was done wrong... You would be surprised how difficult it is to cut a bar parallel when it is sticking out of the spindle unsupported...

RC, I'm just following the instructions in the Textbook of Turning and Harold Hall's book which are effectively the same.

As I understand it, getting the tailstock bore concentric with the spindle (and thus turning parallel between centres) is my next job to be done after sorting out my parallel turning issue.

If you think I've done the cut "wrong", I'd be happy to take some advice on how to do it "right".

Mike, thanks for the tip with the builders level, I've give it a go when I can get back in the shed.

Hi RC,
I think Matt means "the tailstock end"(at least I hope thats what he means)

Hi Matt,
25mm to 22mm in 7 cuts is 0.4mm(0.2mmdoc, 0.008" if you like), I'd say thats a pretty heavy cut for what you are trying to do. Have you tried a lighter cut? Are you using powerfeed? HSS or carbide?
The thing I dont like about starting with this method is it assumes all other parts of the lathe, tool and operation are spot on and that bed twist is the only problem.

Stuart

+1 on the builders level, I used one for years before my ebay days.

Dave

Originally Posted by Stustoys

Hi RC,
I think Matt means "the tailstock end"(at least I hope thats what he means)

Yes I dunno..... Hercus lathes the headstock sits on the tailstock V so it cannot simply come out of alignment anyway...

The fact the taper is not consistent means something else is in play here...

Hi RC,
"made some 5 thou shims, placing one each to the left and right of the front tailstock mounting bolt."
Surely he means the bed? I'm sure he will turn up soon and clear it up

I'm guessing his is using a 0.01mm mic(not that I have anything against them most of mine are, just that there will likely be some noise in the numbers). With deflection over the top of any misalignment you could end up with some pretty funny "curves".

Stuart

I cant see anything wrong with the measurement seems consitent to me.