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Thread: Challenges with New Lathe
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2nd Feb 2020, 08:34 PM #1Novice
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Challenges with New Lathe
Well guys - I survived installing the new lathe and am now making all the mistakes I made 60 years ago when I used a lathe in school !!
Have bought a H and F Optimum 2506V which seems to be a mixed bag.. just have to keep reminding myself that it is basic but so is the price !
- My first surprise was when setting up to change gears, wondered what the mysterious grit was all over the ones installed and those in the bag. Turned out to be sand - so a few hours of cleaning ensued !
- Second having got basic turning working, decided to do a taper using the compound slide - started the setup by checking the accuracy of the dial on the slide and found out it was out. With the slide set on zero, got a taper of around 1mm in a 40 mm section. Spoke to H and F who said just to remark the line for zero on the slide - not terribly impressed !!
- I then started on screw-cutting - have memories of crashing the tool into the chuck at school when I didn't get to disengage the half nut in time and the slowest speed is 150 rpm - so went on You Tube and found a couple of brilliant videos showing manufacture and use of a hand crank to do short threads
- https://www.homemadetools.net/forum/...7799#post37681
- https://www.youtube.com/watch?v=ksCd9FfjUFQ&t=189s
- The result of the above was that I made a rough version of the hand crank then cut a half decent thread in a section of brass bar.
Now the problem
- I have had two or three goes at cutting a thread under power, (using a long test piece to keep me away from the chuck ! ).
- I have made a thread cutting tool from HHS and also tried a carbide tool that came with the lathe
- I have checked the thread indicator gear and that is correctly engaged
- The tool is locked in tight and the 60 degree is at right angles to the work and at centre height
- I have the speed set at around 400 rpm
- I am using a 20mm brass bar that I have turned down to 18mm to cut a M18 with 2.5mm pitch - all the gearing is correct as per the charts on the lathe to give 2.5mm
- I start up, engage the half nut and when I do a scratch cut the thread pitch is correct ( I have my dads old thread gauges).
- When I go back to do a shallow second cut ( engaging the half nut at the same number), the tool does not engage in the same place and makes a second track ( also at 2.5mm)
- What are the likely issues I should be looking for ???
Thanks
Rumble
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2nd Feb 2020, 08:56 PM #2Most Valued Member
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Can you confirm what worm wheel / gear is engaging on the lead screw in the chasing dial , and what numbers are you engaging on and how far past the end of your shaft are you engaging the half nuts to do your subsequent passes.
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2nd Feb 2020, 09:01 PM #3Most Valued Member
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new Lathe
hi mate how fun for you.
400 rpm far out seems fast can you say 150 .using the hss.
Is the gear for your threading dial ungraded properly to the lead screw?
looks like it pivots on axis away or toward the lead screw.
Have you tried stopping the spindle withdrawing the tool and reversing the machine.
aaron
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2nd Feb 2020, 09:39 PM #4
Hi, I am not at all familiar with your lathe, so I downloaded the manual from H&F and looked through it. No mention of the treading dial at all, including the parts diags and lists.
However, it is common for thread dials for lathes with metric lead screws to have multiple gears to engage the lead screw, so I kept poking around and leafed through the collection of photos of the lathe on the site. I believe pic 19 of 29 holds the clue to your problem.
For the threading dial to work for 2.5mm pitch, you need the 30 tooth engaging gear fitted to the spindle of the threading dial, and you can engage the half nuts when the dial markings of 4 or 8 are opposite the reference pin. If you have the other gear fitted to the spindle of the threading dial, the timing between the headstock spindle and leadscrew, would not be affected, but the timing between the leadscrew and the dial indication would be, resulting in threads with multiple starts.
4_Indicator-Table.jpg
To interpret table in photo 19, you need to find the row that lists the required thread pitch, them move to the column that has digits in it. These are the marked points on the dial where you can engage the half nuts. You then move up that column to the second row, which says which gear you need to have engaged with the leadscrew for reliable single start threading. The P=3mm Mn =1 above the gear tooth count indicates that the data is for a leadscrew with 3mm pitch and 1 start (Mn=1).
The only thread pitch where the engaging gear does not matter is 1.5mm (half of leadscrew pitch). This occurs because both engaging gear options listed are divisible by 2, the only common factor for the gears available.
Hope you can understand this explanation, come back if you need more help.I used to be an engineer, I'm not an engineer any more, but on the really good days I can remember when I was.
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2nd Feb 2020, 11:16 PM #5Novice
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Solution
Guys
Malb hit this on the head
I had not seen the table he found - to be frank the manual is pretty naff and I didnt see this
The 30 tooth gear will go on in the morning ad feel sure we will be in business
Rumble
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2nd Feb 2020, 11:51 PM #6Novice
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Sorry
Didnt respond to the other comments
- The thread indicator does engage - just as per the note from Malb - its the wrong gear
- Speed is not an issue - am using brass and the thread cuts fine - just too many of them !!!
- I have tried the alternate method of leaving the split nut engaged, stopping the machine, withdrawing the tool, then reversing back to the start. This also works fine its just a pain !
Rumble
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3rd Feb 2020, 04:29 AM #7
Hi Rumble, Guys,
I tend to try and thread from the rear with the lathe running in reverse ! This means that you are threading away from the chuck. No chance of running the tool into it.
Since I struggle with grinding single point thread cutting tools, I buy and use carbide inserts. The same holder takes both 55 and 60 degree thread angle inserts.
13-01-2019-015.JPG
Cutting a thread in reverse.Best Regards:
Baron J.
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4th Feb 2020, 05:06 PM #8Member
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- Sydney
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Just out of curiosity - did you lock the carriage when you turned a taper with the compound? It's always possible that the gibs are loose and the cross-slide is moving. H&F like to ship you the demo unit on the floor and then order a new one in for stock, and they also like to leave the gibs loose on the floor units so they feel nice to turn. The Optimum 2506Vs generally have a good reputation, so it's disappointing if you got a bad one. Ditto for the compound gibs.
If there was sand in the change gears I'd change the head oil real quick!
Phil
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4th Feb 2020, 08:54 PM #9Novice
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4th Feb 2020, 09:56 PM #10Banned
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5th Feb 2020, 03:58 AM #11
Hi YBAF, Guys,
My lathe is a Myford S7LB, it does have a screw on chuck. Whilst I do thread in reverse using the three and four jaw chucks, I also use a collet chuck which is an MT2 taper fitted in the spindle with a drawbar. I've never had an instance of the chuck unscrewing, though I've heard many stories of chucks becoming unscrewed and chasing the operator across the workshop.
Though I do know of one chap who was parting off with the lathe in reverse using a parting tool upside down and it dug in stopping the chuck and it landing on the cross slide smashing into the toolpost before bouncing down the back of the lathe.Best Regards:
Baron J.
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5th Feb 2020, 06:27 AM #12Senior Member
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5th Feb 2020, 07:53 PM #13Most Valued Member
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Depending on the job and the room, I use both HSS and cardibe threading inserts. Compared to HSS, the carbide inserts are a "gift". They are so easy to set up and use. Both 60 and 55 degree inserts fit on the same tool. It's just too easy. I don't even both setting the compound to half the thread angle, I just plunge cut most of the time.
Having said that, there's nothing more rewarding than grinding your own HSS tool and having it cut like butter! Especially given the challenges I faced when I first started to learn.
SimonGirl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.
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5th Feb 2020, 09:35 PM #14
There would be quite a difference in the amount of torque being coupled from the spindle thread to the chuck thread between reverse threading and reverse parting as hobbyist threading is normally using quite light cuts and trying to sneak to the appropriate depth of thread, whereas parting is normally a case of feed in as hard as the machine can stand without chatter. Obviously not an issue for either operation in the forward direction, as the torque is winding the chuck onto the registers on the spindle.
I know of a couple of people using Myfords that have torn out the T slots at the back of the crosslide using rear parting tool blocks with inverted tools and the spindle running in the normal direction in an attempt to save on tool changes and avoid unscrewing the chuck. Apparently the castings just don't like the cutting forces being transferred to the cross slide in the wrong direction. Someone wrote an article in Model Engineer back in the 1980's advocating this, and there were a number reported torn T slots over the next couple of issues.I used to be an engineer, I'm not an engineer any more, but on the really good days I can remember when I was.
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5th Feb 2020, 09:59 PM #15Philomath in training
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Personally I prefer to use HSS for threading, just because the rpm's needed are less and so the feed is correspondingly slower - more time to pull out at the end of the pass. I used to sharpen threading tools by hand but these days usually use a jig to get the angle symmetric and the correct size/ shape.
I understand wanting to 'do' things rather than mucking around with less exciting stuff like sharpening tools (I've been there too and sometimes, still am), but at the same time would point out to those starting this strangely addictive hobby that unless you spend the time doing the difficult & boring stuff, you won't learn. As Simon says, that feeling when you first sharpen a tool and it works as it is meant to is magic. I don't think I've ever threaded in reverse. I've had some crashes, yes, but provided you learn from them, you will come out a better machinist.
Enough of my ramblings...
Michael
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