Viceroy TDS1 PCS

[superflyguy]

Thank you for accepting me to the group, I have had the lathe for 10yr and only ever played with it a few times. Not sure is this is a limited run machine as I can’t find any info regarding the POS version. Basically its an only imperial machine with power feed, which also works the cross slide. Also has thread cutting feed rod. and I’m hoping to find some detail as I would like to cut metric threads. I’ve got lots of gears for the thread cutter settings just need some help to find out what I need for the metric cuts, the thread feed is 8 threads per inch. Sorry I’m new to lathe work have not really touched a lathe for 30yr.
This is the same lathe as I have.

[DavidB]

For cutting metric threads on the lathe with 100% accuracy you need a 100 and 127 tooth gear but there are some other combinations which are close enough that for most practical purposes they're fine. There are a number of online pages that can do the calculations to work out suitable combinations given your gear set and leadscrew pitch, a number turned up searching for 'cutting metric thread on inch lathe calculator' , you might have a look here https://www.lathes.co.uk/latheparts/page14.html which has links to downloadable software to do the calculations. I've not needed to use any as my Harrison M300 does both metric and inch natively in the feed box, I presume it uses one of the very close approximations, the main thing to remember as it's an inch leadscrew is to not release the halfnuts when cutting metric threads but the M300 can reverse so it's not an issue to back out for the next cut. Some more good information here https://conradhoffman.com/metricthreading.htm

[Pete.]

As David wrote above the perfect translation for imperial to metric threads is using a 127 tooth gear. However, there are a number of combinations which produce an error that is smaller than the typical error tolerance in a leadscrew (not to mention any wear that might be present), so for all practical purposes they can be considered perfectly adequate. Indeed, many manufacturers do the translation without using 127 teeth.

How you go about it depends greatly on what gear set you have. You vcan use a small utility called nthreadp from David's link above to list your gears and it will spit out a close solution for you.

[superflyguy]

Thank you for your help I downloaded the program and I thought I’d start by what was left set up on the lathe from the last owner. it looks like he was trying to cut a 72 TPI thread here are the pictures of the gears. I’m trying to understand when the program tells me what gears and where the gears need to go. But for some reason the 80t gear dose not show up as being needed in the software.I don’t understand the difference between the driver and driven gears
Does it matter which way round they go my guess would be if the 80 tooth and 54 teeth are the opposite way round you still end up with the same result or am I wrong.

Ok I've add a picture that explains the D gear 80t. But the software suggested order is not the same as my setup, dose this matter
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[Pete.]

Okay,

The driver gears are any gear that drives another. The driven gear is any gear that is driven by another. Any gear that both drives, and is driven is called an idler. Idlers are just space-fillers, you can fit any size gear so long as it fits in the space available.

In your pic the 24T Stud gear, the 18T gear are drivers, The 72T and 54T gears are driven, the 80T is an idler.

In a simple gear train ONLY the first and last gears, plus any compound gears count towards the ratio. So you can't change the first, the last or the compound without the ratio changing.

That said, you CAN move stuff about if you follow some simple rules:

Any driver can swap places with any other driver without the ratio changing.
Any driven can be swapped with any driven without the ratio changing.
Any driver can be swapped for a gear with a different number of teeth PROVIDED that any driven is changed by the same ratio, without the overall ratio changing. This would be handy if for instance you didn't have a 54T gear, but you did have a 72. You could use the 72 instead of the 54 as a driven gear (54x4/3=72) so long as you applied the same ratio to any driver i.e the 24T stud gear (24/3x4=32) would be changed by fitting a 32T stud.

[DavidB]

The first driver gear doesn't seem to be taken into account, the one on the end of the lathe spindle and the 28 tooth? forward/reverse feed? intermediates directly after it before the stud gear, they will effect the overall ratio. The lathes.co.uk information does call the gear on the end of the spindle a stud gear. I suspect the first drive gear on the end of the spindle and the intermediates just after it aren't shown on the gear set-up diagram as they likely can't be changed. Just noticed the other gear behind the 24 tooth stud gear, how many teeth does that have? Just thinking if the gear behind the 24 tooth has the same number of teeth as that on the end of the spindle then they would cancel out and the 24 tooth stud gear would be the first in the chain so need to check those other gear numbers.

[Pete.]

Pretty sure that on the non-gearbox models the spindle gear and the gear behind the stud gear are similar tooth count. The gearing chart in the pic above certainly suggests so.

[superflyguy]

I’ve just checked and yes The gearbox gear has 38 teeth and the gear behind the also is 38. I’m not too sure why am so concerned with cutting my threads in metric as it will probably be easier to use taps and dies and for anything larger so long as the two parts I make have the same thread I don’t suppose it matters if that’s Imperial or metric. Thank you for everybody’s help and now understand what the program NthreadsP is telling me. Hopefully
An error of %0.7 should not cause took much problems.
I guess it’s time for me to play with the machine Anna and try and make a wobble Engine my first project. Or would you guys suggest anything else for a beginner.

[Pete.]

0.7% is 7 thou over an inch so if you have say a 16 tpi nut with 8 turns that's less than 4 thou error over the length of the nut - nothing at all for a normal fastener.