Harrison M300 lathe - Experimenting with single point threading

I cut some external threads repeatedly so as to train myself to operate the controls reliably. I also discuss partial and full profile threading inserts, and thread micrometers. I also do some experiments on the actual thread pitch obtained via the M300's feed gearbox.

[@jonathancrossley6803]

Hello, Interesting video - I have an M300 long bed and they are excellent machines - one of the reasons they're still being manufactured. However, I'm slightly perplexed by your pitch variation cutting a 1.25mm thread. Your M300 looks to be a metric machine, and that should have a 6mm pitch main lead-screw and therefore a spindle to lead-screw reduction of 6/1.25 = 4.8 is required. You can check this by marking and counting spindle to lead-screw revolutions, 24 revs of spindle = 5 revs of the lead-screw and so on.

[@samuelfielder]

Thanks. I don't think the pitch varies, rather I think it is cutting a pitch of 1.2474 when the gearbox is set for a pitch of 1.25 mm. That gives a reduction of 4.81 . My thought when I made this video was that even with a metric lead screw not all pitches are necessarily exactly correct, depending upon how well the gearbox is designed and how many gears it has in it. However, reviewing my video of the gearbox refurb, and trying to see what gears are engaged on a setting of 1.25mm = BS3W (this is hard to do), but it seems to be 44/96 * 44/88 * 19/19 * 23/23 * 20/22 * 36/36 and this does come to exactly 4.80 reduction. So I'm now as perplexed as you are. I have to explain (a) why the thread locks up on the long nut that I cut with a tap, and (b) why my measurements with a tape measure produce the wrong gradient (it needs a systematic measurement error of 0.7mm over 324 mm of tape which seems unlikely). Oh dear, back to the drawing board.

[@jonathancrossley6803]

@@samuelfielder Did you try the long nut both ways round? It's quite possible that had a tapered thread towards one end if the tap was not run far enough through

[@samuelfielder]

@@jonathancrossley6803 No, I ran the tap through from both ends.

[@samuelfielder]

I measured the o/d of the male thread I had just turned and it slightly reduced towards the chuck which if anything would make the thread looser on the nut. Also, I parted off the righthand 1cm of thread whilst the part was still in the chuck, and then the long nut went on smoothly over the thread where it was previously stuck. I thought this tended to confirm my hypothesis of pitch mismatch between male and female threads.

[@samuelfielder]

I've just counted the teeth on the change gears: they are correct 44/96/44/88. I think this leaves only two possibilities: (1) the lead screw pitch is slightly less than 6 mm throughout, or (2) some incredible mixup when I reassembled the gearbox, putting the gears in the wrong order on the shaft. Both are hard to credit. The difference, as measured on my tape measure test, is 0.2% which is pretty small.

[@richardjones38]

The cross slide backlash is adjustable, as long as your nuts are not as worn out as mine were. Harrison used at least two adjustment mechanisms / nut designs over the years. Mine (actually a very obscure T300 - the M300 based one not the smaller M230 based T series) has a split bronze nut with a tapered steel wedge between them. I replaced them with brass ones made by an ebay seller in the UK, which cost a fraction of the absurd price 600 group wanted for them. I had intended to have a go at making them - until I discovered that the lead screw on the metric versions is an imperial diameter acme-like thread, but with a metric pitch! The guy who made my new nuts had had a tap ground specifically for making them, and they fitted perfectly. My T300 is unusual in that it is a purely metric machine in terms of thread cutting. It has a different screw cutting gearbox with only two knobs instead of the usual 3 on an M300. This is annoying when I occasionally want to make imperial parts (typically when repairing bits of old machines - everything I intend to work on is metric). But hopefully my simplified metric only screw cutting gearbox cuts the exact pitches I select. I've never found a pitch mismatch like you have here, but then I don't cut threads very often either. I agree that thread wires are very fiddly, but they have the advantage of automatically finding the maximum diameter. Try holding two or all of them to the thread with a rubber band before taking the measurement. I also agree with the other comments saying that starting with a diameter of 10.0 is too big. M10 x 1.25 is a thread I'm very familiar with (it's the standard M10 size on Japanese cars). If you measure commercial thread rolled M10 x 1.25 bolts, the overall diameter is typically between 9.75 and 9.85mm.

[@DKT1st]

Thanks, I found this video contained useful info . I intend to do some threading in the future.

[@smallcnclathes]

When I started with cnc back in 2005, I was amazed that full profile inserts existed (I was a draughtsman at the time) and I embraced them immediately, as I had nightmares about wire brushing every thread I cut! I bought a thread GO gauge for 10x1.0, I found that 9.95 was about as large as a thread could be, for it to wind on at all, with 9.90 being a far more reasonable thread fit. I think it needs to be remembered that the figures in the book are the theoretical figures for the thread. If you make a 10.00 hole and want to fit a 10.00 plug, you will need a quite large hammer! Size for Size is not really a slide fit. For the many thousands of threads I have cut, I have always used say 9.94 to 9.90 for 10.0 thread and similar percentage reduction for any size thread. Never had any complaints about the threads I have cut. Now this is KZbin, so I had better say that is this is my experience and others may say it is a complete load of rubbish. Oh and the advantage of full form inserts is that I have only ever spent money on that one set of gauges for M10. No messing with wires or thread micrometer, only ever measured the thread OD. Any commercial M10 thread I have measured has not exceeded 9.90 and lets face it they do manage to hold a lot of parts together.

[@samuelfielder]

Thanks. I think you are right that the easiest way is to use a full profile insert and just focus on the final o/d of the thread. The o/d of my commercial M10 bolt is 9.87 mm, which I thought was a bit small - and loose.

[@smallcnclathes]

@@samuelfielder yes it is a bit loose, but as I said they work pretty well at holding things together. I think 9.87 would be pretty common on commercial bolts, buy your little exercise has shown that it does not take much more to create a quite firm fitting thread. I love how you manage to throw a graph into a video every now and then. For us Excel dummies how about a tutorial on how to do that?

[@samuelfielder]

@@smallcnclathes I'll think about it.

[@smallcnclathes]

@@samuelfielder don’t think about it too hard, tis only KZbin. No worries, if it proves difficult or time consuming. It could easily eat up time.

[@andrewdolinskiatcarpathian]

Hi Samuel. Fabulous experiments. Very interesting indeed. Thank you for sharing. 👏👏👍😀

[@chrisstephens6673]

To save the maths you can keep the top slide in its normal position, zero on the protractor, and just go straight in with the cross slide, especially ehen using full form inserts. Some years ago i did some experiments to prove what i thought, that messing about with the top slide was poimtles on all but enormous pitches, and even under a microscope the difference between radial and flank feed was impossible to detect. 1.25mm pitch is one of the awkward threads on a 6mm pitch lead screw, on my Colchester Bantam with a 6mm lesdscrew i have to keep the half nuts engaged all the time and have to run the lathe in reverse to get back to the beginning. On threads that can be divided into 6 i can engage the half nuts at any point. Just to finish your testing, try to cut a thread with the half nuts engaged, it may sound illogical but if all the gesrs remain in the same alignment/medhing it might make a difference. It seems that in countries that have been metric longer than us, it is quite common to reverse the lathe aftr each cut, even when cutting a divisor of 6mm, do they know something we have yet to learn?

[@samuelfielder]

Thanks. I'm thinking that the reason for angling the top slide is to reduce the contact area of the tool with the work., which in turn should reduce chatter. So this might be more useful on small or less rigid lathes.

[@chrisstephens6673]

@@samuelfielder certainly flank feeding is less strain but you have a pro quality lathe that is capable of a decent cut. Also your inserts have rake/chip breaker on both flanks so are obviously intended to cut on both flanks. Keeping the top slide in line with the axis is more rigid for things like parting as the dovetail slides have less play than a worn top slide leadscrew. Keeping the top slide screwed hard to the right I find can also help rigidity when parting.

[@stevechambers9166]

Very interesting the way you sorted that pitch variation. That mics got to be a bargain you just need to get used to it. That size change near the chuck it’s something you have to deal with every lathe I’ve used has been like that (I’ve never been lucky enough to use a brand new one) but some haven’t been completely worn out lol coming up to 45years in the trade By the way we have the same m300 lathe as you at work and that strip down and rebuild you did on yours was very helpful with a problem we had thanks for your time👍👍👍👍

[@NightsReign]

Accepting that I'm commenting a year and a half late, have you since worked out from where the taper you were cutting originated? If so, then you can just disregard the rest of this comment. Do you have the tools necessary to measure the runout on that 3-jaw chuck (or perhaps your spindle)? I thought I was detecting the slightest bit of runout at the end of the work as it spun, before you began threading. I can't be certain, as there isn't much uncut time in the video with the work spinning freely and you aren't threading, and what I'm seeing might be actually be video artifacting, or the camera might not be 100% stable. Alternatively, when doing a facing operation, does it cleanly smooth out the surface all the way to the very center of the work, or is there still a nub remaining (it might actually be incredibly slight)? I'm asking because that would indicate your tool holder is slightly beneath or proud of the center line. One or both of these scenarios would definitely contribute to your lathe inadvertently cutting a taper.

[@iansnowdon4949]

Hi Having watched your video and seen the problems you are having I would suggest watching Joe pie video on you tube lathe leveling. I had a few issues when I bought my M300 regarding taper alignment . I've suggested Joe's video as he explains what to look for better than I could put into words. One thing I would suggest as a rough quick guide regarding centres and tail stock. If you put a dti on the end of your stock and entre the tail stock and centre slowly in to a centred hole any deviation will show itself

[@samuelfielder]

Thanks but I'm afraid the problem is not caused by out of level but by excessive wear on the ways. I did cover this in two earlier videos, e.g. kzbin.info/www/bejne/hKPTgmRnmpdqqK8 but there's no need to watch them!

[@lesthompson5907]

i must say i ham interesting in alternative signal pint threading & it astonishing how meny lath are out there that cannot signal pint third because they have no lead screw & A Absent trading gage . Although the lath have the gearing to thread cut but with no lead screw. we have to consider a alternative rout For me this was the ues of the rack as the led screw & a dial designed to mimic that used on the lead screw this resulted in a vert good thread at 8 trad's to the inch . Conclusion though having a led screw & third dial is prefers once one exsep if one dos not have the means we can cut a respectable third by using the rack as a led screw in place of the lead screw.. I through you would find this point interesting . Les England

[@daveharriman2756]

Nice to see you back on the lathe, looks like you ended up getting a decent thread, I love your deduction and logic, watching a few videos about single point threading, there are a couple of youtubers, Stefan Gotteswinter and Joe Pie that do not use the compound slide at 29 degrees, they do it at zero, they maintain that it makes no difference, maybe you could try that as an experiment, I would be interested to know what you think, especially with your logical steps to get to this point. I am yet to try threading on my lathe, as I am new at it like you, cheers, Dave

[@ericfeatherstone]

For the missing micrometer tips Insize 7385 **might** be the right style for Mitutoyo thread mics. T100 series for 60 degree tips & T200 series for 55 degree tips. Similarly Insize 7384 for Tesa mics (I think) and Insize 7381 for Moore & Wright mics. Might be cheaper than Mitutoyo tips; just a thought.

[@samuelfielder]

Thanks.

[@ericfeatherstone]

@@samuelfielder I've done a bit more googling and need to make a correction! INSIZE 7385 are for *internal* thread micrometers.

[@lesthompson5907]

tubal can as a grat fix to that problem by fitting a dovetail clamp to the sandal & setting it with a bolt. win in to the stop set a 0 & out to stop to clear third's or visor verse berending on the lath & proses IT work well Yo can forget the acracy of the Zeros point & just inches your cut as required . At the end o evry cut third reining the cut with no increace to remove metrical because of deflection is unessersery . to stop trends binding . les England. interesting concept you have.

[@markfoster6986]

Have you considered that the problem might be your tapped female part?,have you used the correct drill,did it drill straight if not the tap will follow the error . I tend to drill slightly bigger by 0.100 mm . I've been in engineering for 44 years and most times theoretical never pans out sometimes you can over think.

[@samuelfielder]

Agree one can over think - one of my faults. Think the female part is ok. Tap went straight through with a tap follower.

[@termlimit]

Great video as always! Where did you buy affordable full profile threading inserts in that quantity? Very jealous.

[@samuelfielder]

From shop-apt.co.uk about six times cheaper than Sandvik-Coromorant. But I only bought one insert for each pitch. So that gives me three chances to break the insert before I need to buy another one.

[@termlimit]

@@samuelfielder Awesome thank you!

[@ahmedal-rasbi7832]

Hi Samuel I was following your posts because recently I bought a second hand Harrison m250 lathe but it miss the full system of cross slide... Do you know from where I can get a used one?

[@samuelfielder]

Sorry, I don't have any M250 contacts, so can only suggest scanning Ebay fron time to time.

[@wizrom3046]

Isnt it a metric leadscrew on the lathe? If it is an imperial leadscrew all the metric threads will be imperfect and the lathe is best suited for making imperial threads. 😥 Any lathe I have seen with a metric leadscrew will do 1.25 mm pitch perfectly, many actually have a 2.5mm pitch leadscrew on small lathes or a 5mm pitch leadscrew on a larger machine.

[@wizrom3046]

Never mind, I just read the comments about your leadscrew discrepancies. Very interesting stuff, hope you get to the bottom of it! 👍

[@samuelfielder]

@@wizrom3046 It is a metric leadscrew with a pitch of 6 mm. The feed gearbox accurately produces a reduction from spindle to leadscrew of 4.8 thus in theory giving a precise 1.25 mm pitch.