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Old 02-10-2013, 11:26 AM   #51
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I did not bother with the hex bar in the end, I came up with a better idea



I have this nice barely used 10mm square toolpost spanner that came with the lathe which courtesy of a QCTP is surplus to requirements.

I had to bore the cap out so the spanner would fit but this is what I came up with



The milling turned out to be pretty easy. I held it in the vice horizontally and worked out how much I had to mill off each side and crept up on it checking the width of the remaining steel. Once I got to the magic number, I locked it all off and then did the other three sides in one pass, aligning the part with a set square held against the milling table. I ended up pushing the part square against the vice and gripping it on the smaller flange which ended up with a few bruises as a result, but I am the only one who will see them!

The Seig uses a high tensile 8.8 grade allen head bolt secured by a pin and I copied the original design which is more complex than it needs to be



I figured if I stuffed up milling the square head, I could use the Seig technique.

Now there is only one problem!



I have never cut a thread on a lathe before! I went down to Hare and Forbes to buy a threading kit and had a few practice goes before I tackled this job and had no luck at all. I might get a chance tomorrow to have another go after a bit more research.

I had trouble with the chasing dial which I did not think was working but it seems to be now. I did quick bit of research and realise now I should have been using the reverse switch rather than the gearbox so I might give it another go on some scrap tomorrow before having a go for real on a part with quite a few hours invested in it.

The last time I made a M12 drawbar, I tried to use a die to cut the thread but I ended bending the drawbar a tad so I want to use the lathe for this thread.

Any metric threading tips are welcomed (my lathe has a metric lead screw)!
I never threaded with a metric leadscrew but I think I can help. what is the leads crew pitch and how many divisions are on the thread wheel?

the spindle reverse method is for imperial leadscrews on metric threads or vise versa. the tool should be disengaged from the thread during spindle reversal to prevent tool breakage but its the most foolproof way to single point when in doubt.

on most lathes you keep the gearbox engaged at all times and the half nut is used to disengage at the end of the thread. (unless you are reversing the spindle to feed back as mentioned earlier). hardinge made nice lathes that were an exception to this and used the feed reverse lever on any thread with no need for a thread wheel but unless you find one used its not worth mentioning.

compound rest should be at 29.5 deg to the right of perpendicular to the ways. (there is only one interpretation for this but still everyone I teach gets it wrong) this way the tool does the cutting on the leading edge which makes better chips and better chip removal than feeding with the cross slide. use the cross slide to retract the cutter for resetting the tool for the next pass. zero the wheel or use an indicator to return to position. if you overshoot pull it back and advance the slide again to take out backlash.

use the compound rest to dial in depth of cut and keep track of cut depth. measure the pitch diameter with a thread mic or the 3-wire method when you depth of cut is maybe 70% the thread pitch then take your finishing passes. if threads were fully triangular the ideal depth of cut would be 100% thread pitch if the direction of feed is parallel to the thread angle but threads are generally incomplete and the nose radius on your tool will vary. refer to the machinery's handbook for 3 wire measuring and specified pitch dia.


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Old 02-10-2013, 06:35 PM   #52
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Not a bad idea Trumpy. I had a look at tthe PDF's on their web site, would 3/8" be OK with you? They don't seem to have much of a range of metric sizes. I can get a price and pick it up on my way home one afternoon as they are not far out of my way.

I think I will also get a length of 12mm rod to practice my threading on but ordinary mild steel from Metalcorp was what I had in mind. You can take half of that too if you are interested. I guess I could get the machining steel for this size too if that appeals to you more.
Rod, any size will come in handy ... lol

Just let me know when and where to pick it up

For easy to machine steel go for 1214 (high sulphur but no lead ), you can't weld it though. 1020 B.M.S. machines OK but it does tend to tear a bit. I haven't tried their 1045K B.M.S. yet (not to be confused with 1045 high carbon steel).

I have a couple of 2m lengths of 12mm rod that I picked up from Bunnings. True mystery steel ... lol ... but I'd definitely go for some 12mm 1214

Send me your email address. I have some PDF's you might like to read, in fact I have thousands of them ... lol


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Old 02-10-2013, 07:30 PM   #53
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Geez, guys thanks for all of the input and a bit from Tubalcain on Youtube (who I have watched a lot), I reckon I will be an expert at this before long

Trumpy, talk about Bunnings mystery steel. I bought a couple of bolts to play with from them yesterday, both have the same product code, one was 4.6 grade and the other was 4.8 grade. And one of them was 5 mm shorter than the other. I buy M12 bolts by the box but they are 8.8 grade which is abit hard to play with. Anyway, I used them to prepare some homework exercises yesterday:



So from here, I will correct the undercut (thanks Ross), do any other turning, set the change gears to threading 1.75 pitch, rotate my compound 29.5 degrees (plus my 1 degree error) and drop the belt onto low speed (60 RPM) and practice until I am confident of doing the drawbar remembering to stop the motor as I get to the undercut, retract the tool with the cross slide and reverse the motor to go back to 0 on the cross slide and increase the cut depth with the compound and do it all again!

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Old 02-10-2013, 07:41 PM   #54
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Default Metric Screw Cutting

Hi Rod, Screwcutting on an all metric lathe is no more difficult than doing it on an imperial machine. Just different.

Some metric lathes have a chasing dial with changeable graduated discs that fit in the top, depending on the pitch you are cutting. Others have no chasing dial, like my Stanko Toolroom Lathe.

With the starting lever on the carriage, it can stop and reverse out in 1 or 2 revs of the spindle at low speeds. A couple of dry runs in fresh air to get a feel for the coasting distance, and away you go. That is with 3ph motors and DOL starting. Lathes with a foot brake are a bit easier.

But watch it on 1ph capacitor start motors. If you hit reverse too quickly it will keep running forwards!!! And you will have one of those crunching panic moments...

As I said before, on this size work you can always stop short and pull it over by hand for the last thread or two.

BTW, if you want a nicely formed thread, you can rough it out by screwcutting on the lathe, then use your die to finish it to size. Very little load and wear on the die and it follows the thread perfectly. Coming up to a shoulder you can turn the die around and use the flat side to get closer. Don't forget the oil...

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Old 02-10-2013, 08:43 PM   #55
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So from here, I will correct the undercut (thanks Ross), do any other turning, set the change gears to threading 1.75 pitch, rotate my compound 29.5 degrees (plus my 1 degree error) and drop the belt onto low speed (60 RPM) and practice until I am confident of doing the drawbar remembering to stop the motor as I get to the undercut, retract the tool with the cross slide and reverse the motor to go back to 0 on the cross slide and increase the cut depth with the compound and do it all again!
By Jove, I think he's got it! Good on ya Rod, and keep us informed of progress...

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Old 02-10-2013, 09:03 PM   #56
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Thread cutting on a lathe with a foot brake is an absolute breeze. With a bit of practice a faster speed can be used giving a better finish. When threading, just stop by using the brake, withdraw the tool and then reverse back to the start and repeat until depth reached.


Paul.

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Old 02-10-2013, 09:28 PM   #57
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By Jove, I think he's got it! Good on ya Rod, and keep us informed of progress...

Regards, RossG.
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Yeh, I hope so, the proof will be in the pudding later in the week. As with most things, you only need to miss one bit to make a stuff up. In my case, I missed the bit where it says "use the motor to reverse" and not really understanding how the half nut lever works as my last lathe was halfnutless!

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Thread cutting on a lathe with a foot brake is an absolute breeze. With a bit of practice a faster speed can be used giving a better finish. When threading, just stop by using the brake, withdraw the tool and then reverse back to the start and repeat until depth reached.

Paul.
Paul, If I could have fitted in an AL336 with the foot brake I would have but unfortunately it was oversize for my tiny shed so I have to live with what I have got.
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Old 02-10-2013, 11:26 PM   #58
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Rod, any size will come in handy ... lol

Just let me know when and where to pick it up

For easy to machine steel go for 1214 (high sulphur but no lead ), you can't weld it though. 1020 B.M.S. machines OK but it does tend to tear a bit. I haven't tried their 1045K B.M.S. yet (not to be confused with 1045 high carbon steel).

I have a couple of 2m lengths of 12mm rod that I picked up from Bunnings. True mystery steel ... lol ... but I'd definitely go for some 12mm 1214

Send me your email address. I have some PDF's you might like to read, in fact I have thousands of them ... lol
Trumpy, I've made an order and you have a PM with details. Their minimum order is $50. Not a bad way to buy stock, maybe we should do a Brisbane Group buy from time to time.
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Old 02-11-2013, 10:40 AM   #59
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Well, got a little bit further today. I widened and deepened the undercut and parted off the tip to get the length right. The undercut is sitting at 9.5mm wide but there is plenty of room to go wider. I am pretty sure that is enough for me to withdraw the crossslide while powering down the lathe at the same time in this distance.



I also went by Bohler Udderholm and collected a bit of steel on the way home from work. I had an interesting commute, but it ended up being not that far out of my way only adding 20 minutes to the trip.



This is some 12mm and 25 mm round as well as a piece of 15.88mm hex in 1214 bright mild steel. In case you are wondering, that is 3/8" just to prove that imperial units are alive and well in a country that adopted metric 30 years or so ago). Bohler Udderholm being a German based company ( I think ) has no imperial measurements anywhere on their web site, so 15.88m it is!

The bad news is that I am told I can't weld this stuff ( might add that my welding skills are not much better than my thread cutting skills!).

The 12mm was only $12 a length but BU have a $50 minimum order and cash sales have to be arranged before 3:00pm but I was able to book it to a credit card over the phone and pick up after 4:00.

Anyway, these all came in 3.6m lengths and Trumpy and I have gone halves in it so we ended up with 1.8m (6') of each size for about $40 each. Now what he does not know is that when he comes over to pick it up later in the week, he has to give me a lesson in thread cutting!

I've got a meeting tomorrow evening so the next installment will be Wednesday. Hopefully, I will have time to get my change gears swapped over some time.

If anybody else in Brisbane wants some stock from BU and don't need metres of it, then I would be in for a shared buy like this and Trumpy may even join in too!

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Old 02-12-2013, 12:54 AM   #60
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I hate to tell ya this Rod ... but 15.88 mm is 5/8 inch not 3/8 inch. 3/8inch = 9.525mm

By the look of those photos I wont have much to teach you ... you already know about keeping the half nuts engaged and reversing the motor etc ... so the only other thing you need to be concerned about is the thread depth. As you are threading, keep an eye on the 'crest' of each thread. The width of the crest will give you a good indication of how deep you are and how close you are to full depth. Having a suitable nut or threaded piece to use as a gauge is also handy.

And yes I would be interested in any bulk buys from BU or the like, so if anyone in Bris is buying stock and they have to buy too much, by all means contact me.



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