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Oldneweng
14th Mar 2016, 03:19 PM
I have started playing around with making adjustment bolts to level my lathe, finally. There are 6 holes threaded M24 x 2mm. I was initially thinking I had very little space to insert these and was thought I would have to lift the lathe to fit them from underneath. There are 60mm high pockets that have the threaded hole at the bottom. Then I had a better look. :doh: The top of the pockets are open to the inside of the cast base. I thought threading to the correct size was going to be a nightmare. I don't have any sort of nut this size.

Some time back I purchased an set of IN/EXT threading tools from Daletools. I bought a 25mm EXT tool as this is the size of my toolpost, or so I understand. The external tool was 1.90mm above centre. :C I had to machine some off. I had put it off for a long time. The main reason I have avoided threading up to now.

I put it in the mill vice and decided to use my 63mm indexable facemill with a 0.50mm cut to start. This did not turn out good. There were sparks flying in every directions and the vibration was so bad that stuff was falling out of the mill stand shelves. :oo: This threading tool was as tough as anything I have machined before. I continued to the end of the cut however. The inserts were not good. :no: I had to turn them around to another corner. This cutter has 5 inserts and is the type that cuts to a shoulder. Probably not the most ideal type. In retrospect I would have got one with angled cutters if I could, but I don't recall seeing any at the time. This was a CTC purchase.

I decided to try my 25mm indexable end mill which required 2 passes. This has 3 inserts. It is the same configuration as the face mill. I did a bit of research, finding a video showing the exact same job using angled insert tho, with sparks going everywhere just like my attempt. Anyway I slowed the spindle speed down and spent quite a bit of time playing with spindle speed and depth of cut. I found 0.20mm was an good acceptable balance. The finish was terrible and there was a huge burr on all sides. There was also a very noticable line at the join of the 2 cuts. It could be felt without much trouble. I took the tool down to about 0.25mm from finish size with the end mill and then changed back to the face mill for the finish cuts. I was taking the threading tool out, fitting it in the lathe toolpost and checking the height with the height setting tool I made a while back. That is one of the best tools I have thought of.:2tsup:

The first cut with the face mill was about 0.10mm and the speed even slower. The finish was good and the burr reduced. This cut did not entirely remove the cut join line down the middle. The next cut of the same amount did tho. I finished off with a 0.05mm cut. The finish can be seen below. The burr peeled off by hand and the surface seems to be quite flat. No detectable rocking, and flat even contact with the mill table when rotating it etc. Seems smooth. :2tsup: I will give it a rub on some wet and dry paper to check. I do need to get a surface plate.

361517


361518

Final size is 0.06mm below centre height. Centre height is 22.0mm on this indicator. That is just an arbitary figure. It does not represent an actual measurement, just the centre of the axis. This indicator provides an exact measurement of how high or low a lathe tool is. I use it constantly. It is very helpful to know how much packing a tool needs under it, although I have marked this figure on all my tool cases so it is easy to set the tool height.

Dean

KBs PensNmore
14th Mar 2016, 08:01 PM
Hi Dean,
Is there an article on here showing how you made the indicator tool? Or did you find the plans elsewhere?
Excellent idea by the way.
Kryn

Oldneweng
14th Mar 2016, 09:23 PM
Hi Dean,
Is there an article on here showing how you made the indicator tool? Or did you find the plans elsewhere?
Excellent idea by the way.
Kryn

Here is the link Kryn.

http://metalworkforums.com/f65/t198320-tool-height-gauge

Rereading it shows my post may be a bit confusing.


The left hand cylinder (Piston) is a very nice fit inside the big Cylinder. It has a slot milled in it to provide a flat edge for the 0.25" square HSS to clamp in.

The larger cylinder has the slot. This allows the HSS piece to slide up and down. The HSS fits into a round hole in the smaller cylinder (piston) and is clamped in there. I had no way to cut a square hole.

The design was my idea.

Dean

Oldneweng
14th Mar 2016, 10:21 PM
I have been thinking about how to cut the threads, measurement wise. I don't have any thread wires, but i thought I might be able to find something that I could use instead. Stainless steel tig welding rods are 1.6mm diam. I fired up my CAD program to draw a thread profile and then work out where 1.6mm fits in the thread. It turns out that a the centre of the 1.6mm circle (welding rod) is 1.6mm straight out from the root of the thread. This gives a measurement across the 3 wires of 25.34mm. This is an absolute measurement tho and requires some allowance for thread clearance.

A short while ago I decided to read up on metric threading on my metric lathe. I found a site that explained what thread pitches could be cut without using the threading dial (engage half nuts anywhere) and what thread pitches can be cut with the dial, or at least how to work it out. As I only have the one 14 tooth gear on my thread dial I found this interesting. It seemed that the majority of common threads could be cut on my lathe according to this information. Of course I cannot find the site now.

I am going to do some working out with a spreadsheet and then prove the results on the lathe with scratch cuts.

Dean

ps I have just checked my thread dial and it appears it has a 16 tooth gear.

KBs PensNmore
15th Mar 2016, 01:47 AM
Thanks for that Dean, I do remember reading that article now, couldn't place it before. Dam KRAFT disease.
Kryn

Oldneweng
15th Mar 2016, 08:29 PM
After some mental exercise I realised I did not need to use a spreadsheet to work out available threads pitches when disengaging the half nuts.

Any thread pitch that can be directly divided into the leadscrew pitch can be cut by engaging the half nuts anywhere. For my lathe this includes 0.20, 0.25, 0.3, 0.5, 0.6, 1.0, 1.5, 2.0, 3.0 and 6mm pitch. The chasing dial only adds 4.0mm to this, unless you consider 8.0mm and 16.0mm. I am hardly likely to cut any of those.

Dean

Oldneweng
20th Mar 2016, 01:37 PM
I have had a piece of 25mm ms in the lathe chuck and turned down to 24mm for about a week, but have been busy elswhere. Generally somewhere cooler. A few days ago I started making a trial thread. First I made that so common mistake of setting the angle on 29 deg which was actually 71 deg. I did a few cuts at this angle then realised the finish was horrible. I then realised that this lathe only has angle measurements of -45 -0 - 45 deg. Not very helpful.

The compound rotation has holes for 3 tightening bolts. 2 each side on "wings" and one under the front of the compound slide. The slide has to be wound back abit to expose this bolt hole. Only the 2 side bolts have been in place since I got the lathe. I decided to do somthing about it. I felt that this bolt, being at the "coal face", so to speak, would help with rigidity. The bolts are placed at 90 deg intervals.

My Nuttall lathe had a cracked T slot under the compound. A small section of the T slot was removed by me because this was raised and causing rocking of the compound. This meant one of the T nuts did not have anything to grab on to. I made a "big" t nut from a slasher blade. It was tough and hard to work. I did not want to repeat this.

I finished up making a nut from an M10 flanged nut. I milled the flange until it was flat and smooth, Took the sides down to fit the slot, then took enough off the top to get the right height. Seems to work. I could not think of anything else to use that was suitable.

I then continued to cut the thread. All went well. The half nut lever was engaged, then disengaged at the end. It worked fine. In my research on cutting threads I read a web page where the author said that this idea of having to keep the half nuts engaged when cutting metric threads on a metric lathe was not totally true and it caused a lot of unnecesary trouble. He then went on to explain. This was the page I could not find later. It is true. Many common threads may be able to be cut. This is the first time I have heard this mentioned.

There is also another method that involves re-engaging the half nuts before the lead screw gets out of registration and reversing the carriage. This enables the half nuts to be disengaged at the end of the cut and the cross slide withdrawn away from the work. It will work with any thread you are able to cut.

When the thread appeared to be close to size I started looking at the measuring. The wire size of 1.6mm was measured with a digital caliper. I had to be more accurate than that. Using a digital mic it became 1.574mm. The measurement across the wires became 25.34mm. This was an absolute figure and required clearance. I have no idea how much. I was thinking of about 0.10 - 0.15mm. After alot of messing about I managed to get a measurement that repeated. I was getting close.

The problem is that I don't know of any way to put the threaded piece back in the lathe after checking the fit. I need to cut the thread to size first time. Hopefully I can use the wires to measure after getting the size by trial and error. I only need to cut a short length of thread to try it.

I then decided to put an indicator behind the compound. In doing so I managed to mess up the registration of cross slide/compound and could not find it again. I may have another go by lining up while actually running the lathe. It doesn't matter, but this is at least a chance to get some practice.

Dean

mahgnia
20th Mar 2016, 02:37 PM
Dean,

Seeing as you have removed the test thread from the lathe, are you able to check the thread in the tapped holes inside of your lathe's cast base?

The three wire measurement method is very fiddly at times!

I generally cut threads on the lathe using the simpler plunge cut method. This allows the compound slide to be used to regain the thread registration if something goes awry, such as a broken tool tip or inadvertent release of the half nuts.

The C6 doesn't have a threading dial, and so I do all my threads using a combination of DC braking, jogging and reversing when threading to a shoulder. HSS tools may be more resilient than carbide when using jogging etc.
Does your lathe have these types of speed control?

Andrew.

Oldneweng
20th Mar 2016, 05:03 PM
Seeing as you have removed the test thread from the lathe, are you able to check the thread in the tapped holes inside of your lathe's cast base?

I hadn't removed it. It wasn't quite to size. See below.


The three wire measurement method is very fiddly at times!

I hadn't noticed this! :D


I generally cut threads on the lathe using the simpler plunge cut method. This allows the compound slide to be used to regain the thread registration if something goes awry, such as a broken tool tip or inadvertent release of the half nuts.

As mentioned previously, there are quite a few threads that can be cut by engaging the half nuts anywhere at all and the tool will be perfectly aligned. This is the same with an imperial lathe cutting imperial threads. I am happy to use this method where it will work. Otherwise I will keep the half nuts engaged or use the method in my last post. I am using an insert tool and replacement of the insert should not affect things too much.


The C6 doesn't have a threading dial, and so I do all my threads using a combination of DC braking, jogging and reversing when threading to a shoulder. HSS tools may be more resilient than carbide when using jogging etc.
Does your lathe have these types of speed control?

My lathe has a 2 speed 3 ph motor run via a VFD. It also has a 4 speed gearbox, so I can get pretty slow speeds and still have plenty of power. I am doing this threading at about 22Hz in slow motor speed and lowest gear and the chuck is doing 105rpm. Pretty easy to control. I do have a very effective mechanical foot brake.

I have just come in from my lastest try. I managed to register the thread faily well, but there is some variations in the threads from my attempts. :rolleyes: I did one cut which seemed to be relatively heavy and decided to take it out and try it. A touch with a file and wire brush made it look much better.

First, I found my thoughts about having access to the holes is not true of all the holes. Only 3 have access from above. 2 are cast in above and the 3rd one has an angled rib/brace(??) above it. I managed to start the thread in the hole, but it soon got tight. This is a dirty hole which has probably never been used. It is also hard to clean out. I used pliers to keep screwing it in until it hit the bottom. It did not take much effort. I was able to turn it by hand after that although it was tight. I could not feel any rocking.

Measuring it I got 25.23mm near the end. I will make another one to this size and try it. For a first thread I think this was a good result.

Dean

Michael G
20th Mar 2016, 06:17 PM
You can take a piece from the lathe, check it and replace but it is a pain in the neck.
Basically what you do after replacing it is run the lathe with the tool clear but the thread cutting train engaged. While the gear train is moving let the lathe coast to a stop (don't disengage the train, using the brake may be alright). Because the lathe has been feeding against the half nuts, that's where it will naturally be when cutting for real. All (understatement) you need to do now is juggle your compound and cross slide screws so that the tool fits neatly in the cut. One of the reasons I like the plunge method of cutting is that all you need to do is adjust the compound to re-sync.
Remember that your wires are measuring somewhere near the PCD, so OD clearance won't affect them. The other thing I like about wires is that if the measurement is say 4 thou over size, it means the thread is 4 thou bigger in diameter - much nicer to work out your in feed.
Michael

mahgnia
20th Mar 2016, 06:20 PM
Dean,

It sounds like you have the dimension you need to aim at for the others now.:2tsup:
That should speed up the process for the others.

Andrew.

Oldneweng
20th Mar 2016, 07:55 PM
Basically what you do after replacing it is run the lathe with the tool clear but the thread cutting train engaged. While the gear train is moving let the lathe coast to a stop (don't disengage the train, using the brake may be alright). Because the lathe has been feeding against the half nuts, that's where it will naturally be when cutting for real.

I tried that to realign, but the problem is that I was very close to finish size and there is some relaxing of the mechanisms involved. I didn't mention that I knew the dial positions but lost count of the number of turns. I also disengaged the QCGB then realised that would not allow me to rotate the chuck by hand and immediately re-engaged it. I don't believe anything moved. The chuck certainly didn't.


Remember that your wires are measuring somewhere near the PCD

Ah, no, not really. That is part of the problem. I have no data for this wire size. The correct size is 1.1430mm wires. All I can measure is the outside distance. I worked out the correct distance with CAD, without allowance and I am comparing the 2. Because there is quite a bit of difference in diameter between my wires and the proper ones, my measurement is nowhere near PCD.


The other thing I like about wires is that if the measurement is say 4 thou over size, it means the thread is 4 thou bigger in diameter - much nicer to work out your in feed.

True. That is what I was working on, but I wanted the indicator to make it easier to get close as I am still finding the use of wires rather difficult. I have resorted to using rubber bands. 25mm is too big. I cannot reach the mic thimble and hold things in place. My hands are not steady enough.



It sounds like you have the dimension you need to aim at for the others now.:2tsup:
That should speed up the process for the others.


That is my hope although I am not convinced I am that close yet due to the variations in readings. I also got a somewhat larger reading from close to the chuck end which would be caused by not taking as many cuts that far along trying to align things. The thread is about 60mm long. I don't need anywhere near that much.

Dean

Michael G
20th Mar 2016, 08:05 PM
... I am still finding the use of wires rather difficult.

Yes, that is one of the draw backs with them. 2 hands versus 3 separate bits of wire plus a micrometer. I've heard some people stick them to a block of wood or something with blu-tak to keep them together; the method I normally resort to is to join the pair with a loop of masking tape - the loop bit is important as that still allows them to move if they need to.

Michael

franco
21st Mar 2016, 01:08 AM
The problem is that I don't know of any way to put the threaded piece back in the lathe after checking the fit.
Dean

FWIW if I know that I will want to remove an externally threaded workpiece to check the fit in an existing threaded hole, I cut the thread with the workpiece between centres if at all possible. Provided the drive dog is not disturbed the thread will be correctly lined up for further cuts when the workpiece is replaced between the centres on the lathe.

Frank.

Oldneweng
21st Mar 2016, 12:17 PM
FWIW if I know that I will want to remove an externally threaded workpiece to check the fit in an existing threaded hole, I cut the thread with the workpiece between centres if at all possible. Provided the drive dog is not disturbed the thread will be correctly lined up for further cuts when the workpiece is replaced between the centres on the lathe.

Frank.

Yes, that is another method that I was going to mention, but there is no room for a lathe dog to rotate. I have maybe 20mm clearance max between the thread (bolt) and the inside edge of the casting and one has maybe 2mm clearance between the bolt and the release spring for the foot brake which is a pretty strong unit, as well. My thought was to make a dog that is very thin to mate with a drive arm of some sort, but it just seemed as though it would add inconsistencies which would negate the precision.

I am thinking about using the ER40 collet chuck to hold the bar for machining, but one issue with this is that the collet pulls in as it tightens, moving the work with it. My plan is to cut 6 flats on the bar first, using my hex collet chuck, then cutting the threads and finally putting a point on the end for floor plate contact.

Any suggestions about the best design here would be welcome.

Dean

Oldneweng
21st Mar 2016, 09:08 PM
I thought I would post pictures to show what I am up against.


361678

Inside under the headstock at the front. The brake return spring is almost touching the stud. Not much more clearance to the outer casting.

361679

The same position from outside. I should have had the stud in for this picture. You can see the threaded hole.

361680

Under the tailstock also at the front. This is a totally blind hole in the casting. The rear one is the same. The whole stud either has to screw in via this hole or from underneath after lifting the 1500kg lathe high enough to do so.


Dean

KBs PensNmore
21st Mar 2016, 10:11 PM
Hi Dean, on the bolt already made, would it be possible to drill a hole in the unthreaded end, heat it red hot and press an allen key into it to give a form of adjustment. For the other bolts, I'd make them like an ordinary bolt and insert it from underneath.
Kryn

BaronJ
22nd Mar 2016, 04:04 AM
Hi Dean,

I've seen something similar before, a short threaded stud with a square machined on one end, the threads running right up to the bottom of the square.

Oldneweng
22nd Mar 2016, 10:20 AM
Hi Dean, on the bolt already made, would it be possible to drill a hole in the unthreaded end, heat it red hot and press an allen key into it to give a form of adjustment. For the other bolts, I'd make them like an ordinary bolt and insert it from underneath.
Kryn

The one I have made was only a trial. I do not intend to use it on the lathe. It was made from ms. I have some rod that I think came from pnematic rams that I was going to try. I hope this is better than ms. I have a few different ones I will play with. If it machines nice I hope it will do the job.

I was hoping to avoid lifting the lathe, but this would not be such a big deal. I have the equipment to do it without any risk. I do want to have everything ready first tho.

My intention was to have a shallow cone on the bottom of the jack bolts to locate in a shallow matching hole in the support plate. The cone would be truncated to avoid the tip bottoming out.

I am thinking about how to make these. I would cut a hex on the end first, machine the thread, cut to length and put the threads in the collet chuck so I can machine the cone on the other end. I hope this will be ok.

Dean

pipeclay
22nd Mar 2016, 06:00 PM
Any reason apart from practice that you wish to machine these screws to a close tolerance?

Oldneweng
22nd Mar 2016, 07:28 PM
I am not trying to machine them to a close tolerance. I just don't really know how much tolerance to allow. As I have said before, the charts for measuring over wires is useless to me because I am using non standard ones.

I just want to make them work and not stuff them up. In other words I am fairly clueless about what I am doing. :no: Threading is not something I have done much of and then a long time ago. The test nut is a bit hard to pick up, especially when the bolt is still in its chuck. :rolleyes:

Dean

Steamwhisperer
23rd Mar 2016, 06:46 AM
Hi Dean
This might help with the wires.
Sorry about the quality but the book is hard to scan.
361691 361692

Phil

BaronJ
23rd Mar 2016, 07:59 AM
Hi Dean,

Do a google for "shopcalc" it has all the info that you need. This is the web address you need below, don't get tricked into a pay site for this. It is OS software.

<http://www.dogcreek.ca/shopcalc/WorkshopCalulator.html>

The site seems to be down at the moment...

I run Linux, so if you want I can send you a copy of mine via PM. There is a windows version, but I don't know if it is the same binary.

Oldneweng
23rd Mar 2016, 11:21 AM
Thanks for the information Phil and Baron. I am looking into these.

Dean

pipeclay
23rd Mar 2016, 12:08 PM
Taking a guess that they are M24x3

Turn your OD to around 23.80/23.90.

If plunging take to a depth of 1.84mm .

If off setting take to a depth of 2.12mm.

For the area you are working in you don't really want the threads to be to close.

The point you talk about on the base may work okay , if you could a swivel type arrangement may work better ( small ball bearing sitting in a dimple in the end of your adjusting bolt as well as a greased dimple in your jacking plate.

Oldneweng
23rd Mar 2016, 12:16 PM
Taking a guess that they are M24x3

Turn your OD to around 23.80/23.90.

If plunging take to a depth of 1.84mm .

If off setting take to a depth of 2.12mm.

For the area you are working in you don't really want the threads to be to close.

The point you talk about on the base may work okay , if you could a swivel type arrangement may work better ( small ball bearing sitting in a dimple in the end of your adjusting bolt as well as a greased dimple in your jacking plate.

It is M24 fine - 2.0mm pitch. Thanks for the info. It would have been useful.

The ball bearing idea sounds like a good idea. Thanks. I have some ball endmills I could use. Have to look at what ball bearings I have. I bought a packet of 8mm a while back for a safety clutch on my mill power feed.

Dean

pipeclay
23rd Mar 2016, 12:19 PM
In that case plunge to 1.22mm or off set go to 1.41mm depth.

Oldneweng
23rd Mar 2016, 03:41 PM
In that case plunge to 1.22mm or off set go to 1.41mm depth.


Thanks. I will give it a go.

Dean