Mini Lathe Rear Tool Post

[egaParticipant @ega]

Have you considered whether a hole or other necessary feature of the design could be used for clamping?

I take it that the four cap screws are inclined downwards slightly? You could also drill dimples to receive the ends of the screws placed so as to pull the work down.

Lots of scope for end stops here.

[Martin ConnellyParticipant @martinconnelly55370]

That lump is not going to be lifted by a fly cutter so it only needs to be restrained to stop lateral movements. For ideas on low clamping look at Wixriyd and WDS web sites.

Martin C

[JasonBModerator @jasonb]

Looks like you have plenty of room to clamp from either end to me.

[Ron LadenParticipant @ronladen17547]

Posted by JasonB on 30/01/2019 18:27:38:

Looks like you have plenty of room to clamp from either end to me.

Why I thought it needed clamping along its length I dont know, anyway the clamping bar made a pair and now end clamped. They seem to work as I cant shift it so should hold ok.

Jason its a HSS cutter and 95mm diameter would you think I would be ok with 150-200 rpm, I can run slower but ideally would like to get the mill up into its power band a bit more.

[JasonBModerator @jasonb]

About 200 would be OK. Personally I would bring the cutter back into the body quite a bit more and swing say 50mm dia and then run around 350rpm.

You will be able to feed faster so it won't take any longer than two slow passes with the larger swing.

[Ron LadenParticipant @ronladen17547]

Posted by JasonB on 31/01/2019 10:05:20:

About 200 would be OK. Personally I would bring the cutter back into the body quite a bit more and swing say 50mm dia and then run around 350rpm.

You will be able to feed faster so it won't take any longer than two slow passes with the larger swing.

Thanks Jason will give that a try.

Ron

[not done it yetParticipant @notdoneityet]

If the block is resting on its middle rather than the ends, I would be checking if it would sit better inverted. It is a standard procedure, with planing timber, that the ends touch the table, not the middle? Different, cutting from the bottom and not the top, but one does have two fixed starting points on the first side?

[egaParticipant @ega]

Posted by not done it yet on 31/01/2019 11:20:50:

It is a standard procedure, with planing timber, that the ends touch the table, not the middle?

I may have misunderstood you but I think that what you are suggesting is incorrect.

Timber overhanded as suggested will result in the front of the workpiece dropping into the gap between the infeed table and the cutter block.

[JasonBModerator @jasonb]

It is correct procedure to do it as NDIY says, you will get a very slight drop into any gap and a bit of snipe results but for the rest of the cut you will only plane the high spots. If you do it convex sidedown it will rock depending on where you apply pressure and stay wonky.

[Ron LadenParticipant @ronladen17547]

Thanks guys thats helpful, I think I am lucky in that the block is reasonably flat. I have checked the block both ways up and the way I first had it seems to be the best face down though not by much. One end has full contact and the other I can get a 0.04mm feeler under one corner but only in about 3mm. At the middle of the block the feeler goes in about 5mm deep and only on one side. I would have thought that pretty good and the side to work from.

[egaParticipant @ega]

Posted by JasonB on 31/01/2019 12:32:33:

It is correct procedure to do it as NDIY says, you will get a very slight drop into any gap and a bit of snipe results but for the rest of the cut you will only plane the high spots. If you do it convex sidedown it will rock depending on where you apply pressure and stay wonky.

Thanks for the correction – something to remember for when the woodshop beomes warmer!

NDIY: sorry I doubted you; in fact, all my reference books support you.

The relevant HSE Woodworking Information Sheet 17 seems not to deal with this point and I think this must be because the issue is one of practicality rather than safety.

[not done it yetParticipant @notdoneityet]

I have machined up a few hundred windows, some staircases and lots of doors/frames, etc, but a long time ago. Someone else put together most of them plus finish sanding etc., I’m glad to say! Must now be thirty years ago.

[Ron LadenParticipant @ronladen17547]

Is it possible that the material in the centre of cast iron bar is different to the material around the edges. I have faced one side with no problems and now cutting the opposite side. It was going well but I now seem to have a band along the middle which is cutting differently, I can tell by the sound of the mill plus the cut looks like its rubbing. I have changed to a carbide tool but it hasnt made any difference. I wondered shall I just carry on hoping I get through it, though I only have another 2mm to go.

Ron

[JasonBModerator @jasonb]

I have noticed it several times with round bar where you can hear a distinct change in the sound of the cut but never found it any more difficult to cut.

[Jeff DaymanParticipant @jeffdayman43397]

Hi Ron, you may originally have been looking for Mitee Bite clamps. Link to the firm's website is below. Several versions to choose from. Good products, used them many times in industry. No connection with the company other than as a user.

https://www.miteebite.com/products/

[HopperParticipant @hopper]

Posted by Ron Laden on 01/02/2019 11:27:48:

Is it possible that the material in the centre of cast iron bar is different to the material around the edges.

Ron

Yes. There is usually a hard "skin" on the outside of the bar and then the material gradually gets softer as you go in towards the centre. To do with, among other things, how quickly it cools off when cast. The middle will stay warm and cool slowly while the outside chills off quickly (relatively speaking).

[SillyOldDufferModerator @sillyoldduffer]

Posted by Ron Laden on 01/02/2019 11:27:48:

Is it possible that the material in the centre of cast iron bar is different to the material around the edges.

…

Ron

Yes. Cheap cast-iron can be very nasty. When making low-tech items like sash-weights all that's necessary is that the metal pours. The mix inside might be more like a xmas pudding than pure cast-iron and be full of slag, blow-holes and other faults.

Cast-iron is also notorious for developing hard-spots when it is cooled too quickly or unevenly. Usually the hardness appears as a thin outer skin but it can effect the internal structure as well.

More care is taken when cast-iron is going to be machined, and the process can be elaborate involving long heat treatment in an oven and careful management of cooling.

More likely than a different material appearing in the iron in your case is that the cutting property of the metal has been effected by a temperature issue during production. Not sure what to recommend if the cutting problem messes you up – I've always been lucky in that patchy finish didn't matter to my cast-iron efforts. I think the textbook answer is to keep the iron at red heat for several hours and then let it cool as slowly as possible – a day or two. Not very practical…

Dave

[Ron LadenParticipant @ronladen17547]

Thank guys, I thought if you have any chilled areas they would be on the outside but what I,m seeing is a strip along the middle of the bar, assuming it is chilled..? A 20-25mm band all around the edges is fine and machines really well but not the centre. I am a bit concerned now as I have T slots and dovetails to cut and if I am going to run into this bad stuff it could well be a problem.

Ron

Edited By Ron Laden on 01/02/2019 14:19:16

[Howard LewisParticipant @howardlewis46836]

If you are really worried, you could stress relieve it. Presumably, you will not want to leave it outside for a couple of years, to weather!

Never tried it, but if possible, cooking in an oven at Mark 6 for a couple of hours and then turning off the gas, and allowing to cool slowly overnight. Ideally, buried in sand from the start, but SWMBO may well have something to say about that!

After, it may have changed shape, so may well need cleaning up on the (now ) machined side before tackling the currently convex one.

If you do decide to live dangerously, and do this, keep us up to date on how you get on!

Howard

[Ron LadenParticipant @ronladen17547]

Thanks Howard but I pushed on and it has improved though not perfect, the centre is certainly not cutting the same as it does out towards the edges. I have had to finish for today but I am cutting the second face and 1mm away from the finished size. I ran the first face over a sheet of 400 paper and it looks ok and quite smooth with a finger test. The second face is cutting better than when I started and if it finishes like the first then it should be ok.

Ron

[Ron LadenParticipant @ronladen17547]

I am about to order an ARC 000 quick change tool post but before I do it would be much appreciated if a user of the 000 can provide me with a dimension. I can see most of the dimensions in the ARC catalogue but I believe the tool post has a base plate and I cant see a dimension for that. What would be really useful is knowing the dimension from the bottom face of the post to the tool seat of a standard tool holder set in its lowest position.

The new cross slide I am making is 7mm higher than the original one and I just wanted to check that there is enough adjustment to achieve correct tool height. Most of my tooling is 8mm and I think I will be ok but it would be good to know before I order.

Many thanks

Ron

[Ron LadenParticipant @ronladen17547]

Stage one of the cross slide done, the cast iron bar is machined to size and it turned out ok, quite square and true. The only error is the thickness (top face to bottom face) which has a 0.0025" run out over 7 inches but I cant see that been an issue. I flycut all of it except the two ends which I did with a 10mm end mill.

Next job, clean the workshop it looks like a coal mine..

[Howard LewisParticipant @howardlewis46836]

Put a powerful magnet into a strong plastic bag, and use that to pick up most of the dust.

When you have it over the waste receptacle, remove the magnet, and gravity should do the rest!

If you do get swarf on the magnet, Blutack makes a consumable means of removing it.

Howard

[Ron LadenParticipant @ronladen17547]

Thanks Howard, what a good idea..

[Ron LadenParticipant @ronladen17547]

The plot thickens, I want to get an ARC 000 QCTP but the extra 7mm of height from the new cross slide will sit it too high and with the tool set at it lowest it will still be too high. So I am thinking of also modifying the top slide and removing the raised section where the tool post sits so the slide is all one level.

Although this removes material from below the post seat my gut feeling is that it wont be detrimental and could possibly be an improvement. The lathe lacks rigidity thats for sure and I have often thought that the raised tool mount doesnt help, I could be wrong of course but thats my thinking at the moment.

[Author]

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