Discouraged Feeds on a Lathe?

[SillyOldDufferModerator @sillyoldduffer]

[SillyOldDufferModerator @sillyoldduffer]

Looking at the gear chart on my metric WM280 lathe today I noticed that some of the available ratios have been struck out:

Sorry about the orientation of the photo but the table shows a line instead of a value for five of the possible self-act settings.

Four possibilities are struck out for gear setting 'C'. By calculation I'd expect these feeds to be 0.008, 0.013, 0.015, and 0.018.

As the gearbox produces the expected output, and the feeds produce a good finish, why does the table omit them?

Thanks,

Dave

Edited By SillyOldDuffer on 09/04/2017 20:03:47

[Thor 🇳🇴Participant @thor]

Hi Dave,

I have a similar lathe (290) and have noticed the same as you have. The fine feeds work and I can even get finer feeds by using different change gears to those listed. I too have wondered why they are omitted.

Thor

[JasonBModerator @jasonb]

Someone thought they were too fine though I do use the C position sometimes when facing large diameters such as flywheels

[Neil WyattModerator @neilwyatt]

They probably think no-one has the patience to cut at such fine rates!

[Nick_GParticipant @nick_g]

.

This has just prompted me to have a nosey at my lathe and low feed rates.

Nick

[SillyOldDufferModerator @sillyoldduffer]

Hmmm, it can't simply be the time taken because the cut rate is very reasonable with the chuck at high rpm. Also, the fine feed theory is sort of contradicted by the 'B' gear example where the missing feed is at the coarse end (1.0mm). And it can't be 'bad practice' because Nick's lathe allows fine feeds.

The mystery deepens!

Dave

[not done it yetParticipant @notdoneityet]

Ask Warco?

[JasonBModerator @jasonb]

The missing "B" of about 1mm/rev would likely stall the machine so that is why that is struck off, Even Nicks industrial geared machine only goes upto 0.6mm/rev.

[Nick_GParticipant @nick_g]

Posted by JasonB on 10/04/2017 07:36:35:

Even Nicks industrial geared machine only goes upto 0.6mm/rev.

.

I could change the 48T gears to larger / smaller to get lower or higher feed rates.

But the reality is I have never used a higher feed than BDF or a lower one than BDG and that is only for cast iron flywheels for a final cut. I find that when using such a low feed rate it's important that the tool is nice and freshly sharpened so that it still actually cuts and not just rubs it's way through.

For general machining it stays around BCF. I don't take deep cuts as I am seldom in a rush.!

As a side note to this I was at my mates industrial workshop last week and he asked me while he was busy to machine down a section of 50mm bar down to 30mm over a short length on one of his Colchesters. As I started to get close to 30mm I tried to get a test finishing cut. It was awful.! ……. I asked he what speed and feed rate I needed to do so. He came over and looked at the settings I had and told me that for that style of tool to 'switch on' I needed to be taking a 2 – 3mm depth of cut with a higher feed rate. A different world eh.?

As I was close to the 30mm and had by this time not got that much depth to play with a HSS tool was used to finish off.

Nick

[Anonymous]

Posted by JasonB on 10/04/2017 07:36:35:

Even Nicks industrial geared machine only goes upto 0.6mm/rev.

Didn't you see the helix of swarf resulting from a 1mm/rev feedrate at the last SCMTEG meeting?

My lathe has feedrates from 0.001" to 0.080" in two ranges, obtained by swapping a pair of gears. As of yet I haven't tried feedrates greater than 0.02" per rev. Largely because that is the maximum feedrate on the low range and I can't be bothered to swap over gears, as opposed to just twiddling knobs. On the other hand I very rarely use less than a 0.004" per rev feedrate.

Andrew

[Neil WyattModerator @neilwyatt]

Posted by JasonB on 10/04/2017 07:36:35:

The missing "B" of about 1mm/rev would likely stall the machine so that is why that is struck off, Even Nicks industrial geared machine only goes up to 0.6mm/rev.

My mini lathe will happily do 16 pi, that's about 1.5mm/rev.

I think it's simply that they don't think it's worth having a whole host of extra-fine feeds. Most change wheel lathes as supplied have a finest feed of about 0.004" or 0.002". The 0.03, 0.06 should be enough for most purposes?

Neil

[JasonBModerator @jasonb]

But would it do 16tpi in one pass as its not really worth having a fast feed if you are only going to take a few thou depth of cut.

I think we can all take off large cuts be it with a high feed or large depth of cut a bit like that 0.250" depth cut I took a while ago but its not something we would generally do day in day out, just a bit of swarf waving really

The very fine feeds are handy as I said on large things like flywheels where the DC variable speed machines may lack a bit of torque when slow speeds are also needed so using that C row of fine feeds means you are removing half the amount of metal that you would using the A range so only need half the effort from the lathe. You can also up the speed which goes some way to compensate for how long it would take the tool to traverse the work.

[Neil WyattModerator @neilwyatt]

I was thinking screwcutting for 16tpi and thought you meant stall the gearbox, not the cut!

Very odd to have 1mm missing as it's the most useful metric thread pitch.

I would want to be able to cut metric threads up to 2mm pitch minimum.

Neil

[Nick_GParticipant @nick_g]

Posted by Neil Wyatt on 10/04/2017 13:15:48:

 

Very odd to have 1mm missing as it's the most useful metric thread pitch.

I would want to be able to cut metric threads up to 2mm pitch minimum.

Neil

.

That is a different chart for the gearbox Neil.

The one that is only applicable when you use the screwcutting half nuts. For normal turning you would not use the half nuts but the clutch. ………. Different feed rates then.

Nick

Edit :-

I think you mean this one for TPI / MM pitch don't you.

Nick 

 

Edited By Nick_G on 10/04/2017 14:40:48

[JasonBModerator @jasonb]

Posted by Neil Wyatt on 10/04/2017 13:15:48:

I was thinking screwcutting for 16tpi and thought you meant stall the gearbox, not the cut!

Very odd to have 1mm missing as it's the most useful metric thread pitch.

I would want to be able to cut metric threads up to 2mm pitch minimum.

Neil

There is a clue in the title Neil, we are talking feeds. Inparticular cross feeds as there is a 2:1 reduction so whatever the feed shaft is doing you will get half the cross feed for any lengthways feed.

The 280 variants do have 1.0mm pitch as well as coarser metric pitches for THREADING.

Edited By JasonB on 10/04/2017 16:06:25

[Anonymous]

Doesn't look like 2:1 ratio in the chart shown in the OP, unless I'm misreading it?

Andrew

[JasonBModerator @jasonb]

Sorry Andrew you are quite right, it is more like 3:1 on my imperial machine but looks to be nearer 8:1 on the OP's chart which is quite strange as the two machines more or less share the same apron parts which is where the reduction is.

[SillyOldDufferModerator @sillyoldduffer]

Interesting comments. I'm thinking Nick (and others) are on the right track suggesting rubbing rather than cutting at fine feeds.

I've not been scientific about it but I have noticed that the combination of feed-rate and depth-of-cut matters. I often get a better finish from deeper cuts : I assume this is because the tool is forced to cut rather than bounce over the surface. Presumably feeding at a low rate is also likely to rub rather than cut as the tool moves sideways.

Although I've been happily lathing for several years now and am much better than I used to be, I don't have a reliable sense of best practice for the types and sizes of material I cut. I have speed / cut recommendations for flooded production work but I don't think I've seen similar for use in a modern amateur workshop, where oriental kit can typically spin a chuck up to 2500 rpm . For example, what speed, DOC and tip type produces a good finish on BMS when dry-cutting on an amateur lathe? Does anyone have a simple table that would help?

As this is a wonderful opportunity to potter while pretending to be useful, I shall play on my lathe tomorrow with different feed rates and see what happens.

Dave

[Neil WyattModerator @neilwyatt]

It's my change-gear mentality, where there's no clear line between screwcutting and threading.

I forgot gearbox lathes usually have two sets of speeds, one for each (or two feedscews on posh ones).

[not done it yetParticipant @notdoneityet]

It's my change-gear mentality, where there's no clear line between screwcutting and threading.

Ahem!

​

Gearbox or change wheels aside, I thought screwcutting and threading have no line between them – at all!

And, btw, it is the better quality lathes which have separate threading lead screw and power feed shafts. Comparison of myford with Raglan comes to mind.

[Michael GilliganParticipant @michaelgilligan61133]

 < no comment >

Edited By Michael Gilligan on 10/04/2017 21:09:48

[not done it yetParticipant @notdoneityet]

Again

So? Raglan was a a far better machine than myford. Myford bought them out and shut them down. Obviously a good move by myford as their lower quality machines were far more popular due to the price.

The 5" was streets ahead of anything myford ever produced, at a guess.

If you've nothing better to add to the thread, you would be better to add nothing at all.

[Anonymous]

Posted by JasonB on 10/04/2017 16:55:50:

Sorry Andrew you are quite right, it is more like 3:1 on my imperial machine but looks to be nearer 8:1 on the OP's chart which is quite strange as the two machines more or less share the same apron parts which is where the reduction is.

Phew, at least that means I'm not going doolally.

Andrew

[JasonBModerator @jasonb]

So my Warco280 must be a good machine as it has the separate feed shaft, I'm happy now it has been confirmed to be better quality than a Myford For the most versatile setup then Hardinge have the right idea with a separate variable speed motor on the apron to give you whatever feed you want irrispective of teh spindle revs.

 

I'm not sure I would like the metric version with an 8:1 difference in cross feed rates to turning cuts. With my imperial one I generally use the C position for turning and flick the lever into A for facing which gives approx similar rates. To do the same on a metric machine would be out of the question without having to swap over change wheels.

J

Edited By JasonB on 11/04/2017 07:29:33

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