Lathework for Beginners

[SillyOldDufferModerator @sillyoldduffer]

Sounds like the arrangement on my old mini-lathe. May not be quite as simple as the two rear screws being locking screws, which is exactly what I thought until I tried adjusting them!

Whether by design or crude manufacture, on mine the four screws worked in concert. As expected the side screws control the major right/left angle. But tightening the rear screws also moved the centre slightly, not only right/left but up/down as well. The effect was to make the tailstock describe a small figure of eight movement as the 4 screws were tightened. I found it a fiddle to get spot on. One of those, nearly right, better, better, better, bugger start again jobs!

Possible that the 8 movement was due to poor finish of the rear block, rather than a deliberate fine adjustment feature. However, as the tailstock was spot on from the factory, they knew how to adjust it in China, as did I after 10 minutes of industrial language. Decided in the end that the tailstock adjustment is a basic cost-saving design that substitutes operator time for ease of use.

Interested to know if you get the same result.

Dave

 

Edited By SillyOldDuffer on 23/06/2018 18:26:30

[Ron LadenParticipant @ronladen17547]

Hi Dave,

Thanks for the advice, it did cross my mind that the rear screws could be for something other than locking screws. I found it odd that the two screws are not equi spaced off the tailstock centre but the pair are offset to one side.

I will wait until I turn a centre in the chuck and have a good play then. I can see how the rear screw nearest the tailstock edge could pivot the tailstock around the underside fixing screw.

Will let you know how I get on.

Ron

[Neil WyattModerator @neilwyatt]

I milled out more space and fitted a brass gib to my tailstock.And replaced the adjustment grub screws with cap heads.

BTW the sprung plunger on the toolpost is a stop to allow you to change tools and return to a position with accuracy. It's reasonably effective.

Neil

[Ron LadenParticipant @ronladen17547]

A question I have been meaning to ask: The gear set I have with the lathe are plastic (nylon I think) should these be lubricated with anything in particular or just general lubricants.

Ron

[Ron LadenParticipant @ronladen17547]

I have both read and been told that the 3 jaw chuck supplied with minilathes is something of a gamble. Some are very good whilst others are not with them well out of true.

Well I must have been lucky or the gods were smiling on me or something. The dial gauge arrived yesterday so I checked the chuck this morning. I first checked the spindle face plate and that had 0.0004" run out so I was very pleased with that figure. I then checked the chuck main body expecting it to worse but it wasnt, it gave the same reading. I then looked for something that would be quite true to check the reading at the jaws, dont have a lot to choose from just yet but used a new medium size centre drill and a new good quality 1/2" tap. I measured both of them on the ground body/shank. To my amazement the run out was 0.0004" for the centre drill and 0.0005" for the tap. To be honest I couldnt believe it would be that good so I put one or two other not so good items up to check the dial gauge was ok and that I wasnt seeing things…lol.

So I am obviously really pleased, I wouldnt imagine you would get much better on a minilathe.

Ron

[JasonBModerator @jasonb]

Ignor this post, I'm just testing something for Ketan.

J

[Neil WyattModerator @neilwyatt]

Posted by Ron Laden on 27/06/2018 10:11:11:

So I am obviously really pleased, I wouldnt imagine you would get much better on a minilathe

I can't say I'm hugely surprised Ron, but be aware that to keep those figures you need to be careful not to overtighten and strain the chuck and to keep it clean!

[Keta SwaParticipant @ketaswa78353]

Test post for Jason, please ignore.

[Ron LadenParticipant @ronladen17547]

Posted by Neil Wyatt on 27/06/2018 11:49:46:

Posted by Ron Laden on 27/06/2018 10:11:11:

So I am obviously really pleased, I wouldnt imagine you would get much better on a minilathe

I can't say I'm hugely surprised Ron, but be aware that to keep those figures you need to be careful not to overtighten and strain the chuck and to keep it clean!

Hi Neil,

I must admit I was very surprised, I have watched a lot of minilathe videos on youtube and some I have seen have had 5-6 thou run out. I thought that if I get half that I would be reasonably happy but to have less than half a thou I,m just delighted.

I will look after it Neil, in fact I,m going to strip the chuck and make sure its clean and well lubricated.

Ron

[Ron LadenParticipant @ronladen17547]

With the chuck checked this afternoon I also set up the tailstock for centre, I have it as true as I can get it.

I then set up the dial gauge on the barrel running from fully in to all the way out both vertically and in the horizontal looking for any deviation off centre but it appears to be spot on through all its travel.

Ron

.

[Ron LadenParticipant @ronladen17547]

Stripped down the 3 jaw and found it to be clean but a little dry, gave it a good lube and made sure it went back to the same position on the spindle face plate. Double checked it with the dial gauge and it is still showing .0004" run out.

Well thats about it for now, all is checked/setup and with the HSS tool set having arrived, time for some serious practice.

Ron

[Mike PooleParticipant @mikepoole82104]

That's an impressive figure for runout Ron, especially if it holds over a range of diameters. Personally I don't worry too much about runout but I am interested in whether the face of the chuck and the face of the steps are true as they are references for facing work that you would like to be parallel.

Mike

[NigeParticipant @nige81730]

Just a heads up about the power feed handle for the saddle and cross slide feed. It is VERY EASY to go straight through the neutral position and straight into the cross slide power feed position when disengaging the saddle power feed as I have found out AGAIN. This happened even though I had practised the gentle movement required and knew the possibilities !!! Fortunately it didn't cause too much damage to the work piece as the lathe stalled as the tool dug in and I was able to get the E. Stop hit.

[NigeParticipant @nige81730]

I was looking at setting the Sieg lathe up to cut a 12 tpi thread and decided to use the method I was taught at school and to angle the compound slide to half the included angle of the thread and wind on all the cuts from there. As this is a Whitworth form thread that gives and angle of 27.5 degrees. To achieve that the compound slide has to be rotated clockwise (looking down on it) 62.5 degrees.

Two problems immediately arose. One- The slide would only rotate about 45 degrees and then something was stopping it. On investigation I found that the head of the backlash adjustment screw under the compound was catching on one of the bolts seen in the photo below.

The answer was to remove the screw and gently file about 1.5 mm from the thread. This leaves ample thread for further adjustment and gets the screw to just clear the bolt head. Below the offending backlash adjusting screw.

Problem Two- Once you rotate the compound round to about 45 degrees you can no longer see the witness mark against which the angle is usually set as it is now hidden under the compound! What is needed is a second witness mark round to the left of the compound against which the angel can be set. Question is what is the best way of making the new mark, maybe a centre punch mark or a scribed line of some sort, if that how please ?

Edited By Nige on 30/06/2018 19:59:40

[NigeParticipant @nige81730]

How does the face plate fit onto the SC4 Please? Does it bolt on the same as the chucks ?

[JasonBModerator @jasonb]

I think its the same as the chucks, 3 or 4 bolts depending on how many holes in the back of the faceplate.

You could scribe a mark on the cross slide or just put a bit of masking tape on and mark where say 40 deg is then just move until 22.5deg lines up with your mark.

[NigeParticipant @nige81730]

Thanks Jason. I wondered if it just bolted on, I couldn't think how else it would fit but I think it is bigger in diameter than the 'back plate' the chucks bolt to so I'm wondering what sort of a struggle it is going to be to get them in

I might sharpen a bit of HSS and see if I can scratch a better mark than I will get with my scribe.

[Ron LadenParticipant @ronladen17547]

Morning guys,

I was up early this morning and had a couple of very pleasant hours on the minilathe.

Nothing too exciting but its so nice producing parts for the loco without having to rely on other people to get parts made. I made 4 chassis tie bars from 3/8" steel bar machined and faced to length and then tapped M4 each end. I then started on 4 suspension spring locators in 1/2" alu bar.

However yesterday was not so good, one of the steel loco wheels has some surface marks on the outer face, nothing too much but I thought I would take a couple of thou off the face to tidy it up. The wheel is a plain disc 82mm diameter across the tyre and it is pressed onto the axle which made it convenient for holding in the 3 jaw.

Using a new HSS knife tool I set about facing the wheel, I thought a 2 thou cut should be about right with maybe a second cut if needed. Being new to this I obviously didnt realise that the tool went blunt almost immediately and was just rubbing not cutting. I added another 2 thou but that just left rough marks on the surface so I stopped. On checking the tool sure enough it had lost its edge and had a rubbing mark down from the tip.

What did I do wrong…?

Was the speed wrong, I had it at 600rpm

I was cutting it dry as I thought with very light cuts it would be ok.

I had set the tool angle to the job so I dont think there was an issue there.

The same tool I sharpened and it was fine on both steel and alu parts I made this morning..?

Regards

Ron

[Mike PooleParticipant @mikepoole82104]

Around 100rpm would be more like the speed for a HSS tool on steel of that diameter.

Mike

[Anonymous]

Posted by Ron Laden on 06/07/2018 09:53:21:

What did I do wrong…?

Was the speed wrong, I had it at 600rpm

Waaaaaay too fast. At the wheel periphery 600rpm corresponds to about 500fpm; that would be pretty sporty even for carbide insert tooling. A general rule of thumb for low carbon steel and HSS tooling is cut around 100fpm. So you need to be running at more like 120rpm.

Holding the wheel by the axle means that the wheel is not able to resist cutting forces very well. Although a 2 thou depth of cut should be ok, you may run into chatter problems.

Andrew

[Ron LadenParticipant @ronladen17547]

Thanks Mike and Andrew.

Well a lesson learnt there.

Thanks again

Ron

[SillyOldDufferModerator @sillyoldduffer]

Useful rule of thumb for cutting speed in steel with HSS is 10000 / diameter of work in mm. Easier than working out feet per minute and will get you in the zone. Multiply answer by 2 or 3 for carbide. 10000/86 = 120rpm.

Learning the appropriate tool geometry, cutting speed, depth and feed for different materials takes time. It's not overly critical but…

Andrew's point about work-holding is also important. Considerable forces are applied when you cut metal, and, given the slightest opportunity, the work will bend and spring back. Best solution is to hold the work rigidly. Where that's not possible, lighter cuts.

Dave

[Ron LadenParticipant @ronladen17547]

Thanks Dave, the 10000 divided by diameter is easy to remember, that will be stuck in my head now.

regards

Ron

[Ron LadenParticipant @ronladen17547]

I have seen recommendations for staying with HSS tooling on the minlathe whilst others seem to use carbide just as often as HSS if not more.

To add to my selection of tooling I got myself and 8mm index tipped tool from Arceuro with a set of the 060-204 tips.

Despite my gouty hand at the moment I gave the new tool a try this morning turning a piece of 10mm steel bar. Just a simple test but it seemed to work fine. I have read that the tipped tools need to work harder so I ran the bar at 1600 rpm, dont know if that was about correct for 10mm bar and a tipped tool but I guessed at it. I gave a finishing cut of 2 thou and it seemed to be a decent finish, probably not quite as good as HSS but ok.

Would appreciate thoughts on the tipped tools and minlathes.

Ron

[SillyOldDufferModerator @sillyoldduffer]

Posted by Ron Laden on 06/07/2018 10:58:13:

Thanks Dave, the 10000 divided by diameter is easy to remember, that will be stuck in my head now.

regards

Ron

It's more respectable guide than it might first appear.

All materials have a recommended cutting speed which is determined by a combination of chip formation and how hot the tool gets. It happens that mild steel and HSS cut best at about 30metres per minute.

So RPM = 30 / pi * diameter (in metres)

By converting metres to mm and taking pi = 3, you get the easy sum:

rpm = 10000 / diameter(mm)

Other common materials cut a bit faster or a bit slower than steel and the sweet spot for a particular job can usually be found nearby by experiment. Multiply rpm by 3 to 6 if using carbide rather than HSS.

A professional shop would find it worthwhile doing a more sophisticated calculation, but for amateur use the shortcut is good enough. It's unusual for an amateur to maximise production rates. We live within the limits of our skills and machines, and have time to tweak for best results from what we have.

Dave

Edited By SillyOldDuffer on 15/07/2018 13:31:55

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