Lathe accesories

Khiraly asked me for a walk through of the lathe accessories I mentioned before, so here goes. I am no expert on lathes, I am learning as I go along. In fact, I learnt quite a lot writing this!

Cutting tools



This is an 11 piece tungsten carbide turning tool set. I had some trouble finding out exactly what each tool is intended for. This diagram, from the McMaster-Carr catalogue, gives a good idea but doesn't exactly match the shapes.



Today I noticed that each tools is stamped with a DIN standard. Googling those mainly came up with German and Scandinavian adverts for the tools, some of them charging $99 for one tool! Eventually I found a German site selling DIN standards. Putting in each number gives the title of the standard, which is the description of the tool.

So from left to right we have: -

1. DIN 4974 R Internal side turning tools for corner work with carbide tips.
2. DIN 4973 R Boring tools with carbide tips.
3. DIN 4980 L Offset side turning tools with carbide tips.
4. DIN 4980 R As above but right handed.
5. DIN 4978 R Offset turning tools for corner work with carbide tips.
6. DIN 4971 R Straight turning tools with carbide tips.
7. DIN 4972 R Bent turning tools with carbide tips.
8. DIN 4977 R Offset face turning tools with carbide tips.
9. DIN 4981 R Parting-off tools with carbide tips.
10. DIN 4976 Wide face square nose tools with carbide tips.
11. DIN 4975 Pointed straight turning tools with carbide tips.

1 & 2 are mounted parallel to the lathe axis and are used to bore out the inside of the workpiece. Each cut would be along the axis and successive cuts would move outwards.

8 would also be mounted parallel to the axis, but with the cut going across the face of the workpiece.

9 is mounted perpendicular to the axis and is driven into the work to cut it off from the stock. I hadn't realised it was a parting off tool, I have happily been using it to turn bearing lands with straight sides. I bought a thinner parting off blade, which wastes less material.



All the other tools are for mounting roughly at right angles to the axis and cutting along the outside of the workpiece.

11 has a 60° point for cutting external threads. I bought a set of gearwheels for cutting metric threads. These alter the speed of the lathe's auto feed to match the thread pitch. The procedure looks a bit complicated though, so I have stuck to using a die so far. It would be nice to be able to make large pitch ACME lead screws but that seems even more complicated.

I have had titanium nitride indexable tools recommended to me for their very long life. They have a three pointed replaceable tip. Each time a tip wears out you can rotate it until they are used up, at which point you replace it. They are quite expensive but replacement tips are not too bad.

You can also buy blank steel tools and grind them to whatever shape you want yourself.

Tools are mounted in the tool post and held down with machine screws :-



The tip of the tool must be at the same height as the centre of work. This is most easily done by aligning it against the tailstock centre. Small differences can be compensated for with the rocker under the tool by tilting it slightly. Large differences would result in the tool at the wrong angle so the other side of the post is used with a shim. The tool should be gripped as close to the working end as possible to prevent chatter.

Compound Slide
The lathe comes with a cross slide that allows you to move the tool across the workpiece and the feed screw allows motion along the axis of the lathe. To be able to cut a taper, and for cutting threads, you need to be able to move at an angle to the lathe's axis. The compound slide replaces the tool post and adds another axis of movement at any desired angle.



The next model up lathe, the CL300M, includes a compound slide, so if you take that into account the price difference is not that much. A lathe without one is quite limited, IMHO.

Drill Vice
I got a tiny quick release drill vice that fits on the cross slide to hold work for drilling or milling. Quick refers to the fact that rather than screw the vice all the way to open it, you lift a ratchet and drop it in the nearest slot for the width you want. Then you use the screw to tighten it no more than a quarter of its maximum travel.



This highlights the main compromise having the lathe, mill, drill combo. The cross slide is wider than normal for a lathe, which limits how close the tailstock can get to the chuck, but small for a milling table or a drill table. Also the height of the cross slide means that the tallest thing you can drill is not as much as you would expect from a pillar drill. If I get desperate I could remove the tailstock and cross slide, move the saddle out of the way and put a board on top of the lathe bed to drill a large object.

Tailstock Chuck
This is just a drill chuck with an MT1 Morse taper to fit into the tailstock quill. It allows you to drill into the center of the work piece. You might think holding the drill stationary and spinning the work is the same as spinning the drill and holding the work. It isn't, the former ensures the hole is exactly down the centre of the workpiece.



The chuck is exactly the same as the one the comes with the milling machine, but annoyingly that and the headstock have MT2 tapers but the tailstock is only MT1. If the tailstock was MT2 it could have shared the chucks with the milling machine, and also many other tailstock attachments, like boring heads and tap holders that only seem to go down to MT2.

Four Jaw Chuck
The lathe comes with a three jaw self-centring chuck. The jaws all move together to hold a round or hexagonal workpiece centrally (within the accuracy of the chuck). To hold a square or octagonal shaped object you need a four jaw chuck. These usually have jaws that move independently allowing / requiring objects to be centred manually. That also allows rectangular objects to be centred and you can also mount things deliberately off centre.



Potentially you can centre round things more accurately than you can with a three jaw chuck but it takes more time and skill.

Large, and or completely irregular shaped things can be held using a faceplate and bolts or clamps.

Milling Chuck
The drill comes with a normal three jaw drill chuck.



A collet chuck provides better centring and grip for milling. Expensive, but the sizes match a set of end mills I already had.



This also fits the headstock, so another way you can mill and drill on a lathe is by using a vertical slide.

Wiggler
This is a special chuck and a set of probes that are used for lining up the drill / mill with centre marks and edges of the workpiece.



The special chuck forms a ball and socket joint with the probe so it can swing. When you spin it in the drill chuck it rotates in a circle, but by pressing on the edge you can persuade it into a mode where it spins dead centre to axis of rotation. You use the point to line up on centre punched holes and the ball and cylinder for finding edges. The bent one is used with a dial indicator but I don't understand how or why.

Instructions for using one are here. The balls are imperial sizes, which is a pain if you are working in metric units. I don't know if you can get metric ones.

Die Holder
This allows tapping an external thread by turning the workpiece in the chuck and holding the die with the tailstock.



The bar goes in the tailstock. The tube slides over it and can be rotated part of a turn with the handle. Different size dies can be used in each end of the holder and the two adaptors allow for two larger sizes.

I could not find one to fit an MT1 tailstock, so I had to get an MT2 one plus an MT1 to MT2 adaptor.



This is far from ideal because it takes up so much of the distance between centres. I ground off the tang at the end of the taper because there is nothing to engage it on my lathe. That gives me about another 10mm. I will probably bore out the end of the die holder's bar so that it will accept an M5 bar inside it. That will allow longer threads to be tapped without weakening it too much.

One other problem with the die holder was that the set screws in it do not have pointed ends. When using split dies the middle screw should have a cone shaped point so that tightening it forces the split open, allowing an oversize thread to be cut. Tightening the outer two makes an undersized thread. When tapping something hard like stainless steel you need to start oversized and then work down.

I solved the problem by turning a point on an M5 setscrew to replace the middle screw.

I should really have made one of these, I think, rather than buying this one that is too big. It should be fairly straightforward to make on a lathe. I don't fancy turning an accurate MT1 taper but you can buy Morse tapers with a soft blank on the end for machining to a custom use.

Centres


The MT1 tailstock centre of the right came with the lathe and is known as a "dead centre" because it does not rotate. The one in the centre is a "live centre" because it has a bearing, which allows it to rotate with the work, reducing the friction. There is also a variant called a "half dead centre" which is a dead centre with half the cone cut away to allow a facing tool to get in.

I also got an MT2 dead centre to fit the headstock or my MT2 adapter.

Some good reference material: -
www.americanmachinetools.com/how_to_use_a_lathe
myweb.tiscali.co.uk/silkstone/minilathe/minilathe01

Hat Rack

I came across this object designed by Gorg Huff in the RepRap objects wiki. It was such an interesting organic shape, completely different from anything else I have printed, that I had to try it.



It was a bit too big for my machine so I scaled it down and printed it diagonally.



It took about 4 hours plus an hour for the raft. Because the sides slope in quite quickly, Skeinforge switches to 100% fill for a lot of the layers because the edges don't have anything two layers above them. This can be fixed by selecting 3 extra shells on sparse layers. That means the infill starts far enough from the edge to have something two layers above it. You get a stronger object with less plastic that way.

Hot Stuff

When I was making the chuck grip I noticed that the raft changed colour part way across the top layer of the raft.



The heater seemed to be on 100%, so it looked like the plastic was way too hot. By the time I noticed it seemed to have reached thermal equilibrium and apart from some snap crackle and pop sounds, and a bit of smoke the extruder seemed happy. I was reluctant to abort the build because it had taken about an hour to get this far.

When it finished the raft it cooled down to the right temperature and built the object. The surface of the raft has a completely different texture and it seemed easier than usual to peel off the object. Despite that, it managed to hold down what was a very big object. The shape of the object was less prone to curling than most, being a large circle (no corners to curl up) split into three segments and with a corrugated outside perimeter, which could absorb shrinkage. I need to do more experiments to know if it is beneficial to deliberately make a raft like this.

This is what the normal and hot rafts look like close up :-

And here they are under a microscope :-


To investigate further I ran a test with the heater target temperature set to 300°C and monitored the thermistor reading. It maxed out at 290°C. That is fortunate as it is just below the point where PTFE is supposed to start decomposing into poisonous substances. For some reason the PTFE holds up mechanically, I would have expected the barrel to pop out. Perhaps the ABS becomes so fluid that there is very little pressure required for extrusion. Anyway, the extruder seems happy operating at 280°C, where it just about manages to control the temperature with 96% PWM.

The filament changes from green and smooth to almost cyan and a rough texture: -


Again under the microscope the surface looks very different :-

My theory as to what is happening is that the green dye is composed of yellow and cyan dyes, and the yellow component is boiling off, disrupting the surface.

I had a go at making some objects at 240°C, 260°C and 280°C :-



It seems that 240°C is about the limit for green ABS before it starts to change colour and texture. The bottom of each object has to be at the correct temperature so it can be separated from the raft but other layers could be chosen to be different temperatures to give a stripy effect. The hot objects seem very strong and feel like they wont de-laminate in a hurry.

I don't think you can keep the plastic long at those temperatures, I found this mess under a raft. I think the temperature had gone wrong during warm up.



Initially I had no idea why my temperature control was occasionally going wrong. The thermistor is still well attached. I caught the effect with some logging and discovered that the temperature was reading about 40°C low some of the time. Touching a connector seemed to fix it. I could not find a loose connection so I just unplugged it and plugged it in again. I has been OK since. With a 10K thermistor you only need a few ohms to make a big difference at the high end.

So an interesting effect that might be exploitable for support material or aesthetic effects.

Key Things

Zach Smith and Bre Pettis have created a web site called Thingiverse, which is designed to make it easy for people to share digital designs of real objects. I have put most of the things I have designed for printing on a RepRap on there. I even created one especially for it, a key for reading utility meters :-





You can get these free from the utility companies, but not a quickly as you can RepRap one for a few pennies worth of plastic, and they are easily lost. The files can be found here :- www.thingiverse.com/thing:88.

I also keep a gallery of all the things I have made with HydraRaptor here: sites.google.com/site/nophead/Home/hydraraptor/ThingsMade. They all now have links back to Thingiverse for the files.

A lot of the objects on Thingiverse are for a laser cutter, but I downloaded this twisted star box designed by Marius Kintel and printed it.





One trick I have learnt is that you can shrink objects a little by heating them with a hot air gun. When I first made this the top was too tight, so I shrank the bottom a little with the heat gun. It is now a perfect fit. You have to be careful not to get it too hot, or it will sag.

New Toy

The company that I have worked at for 25 years gave me a long service award recently. I could choose anything worth £500 so I chose this small lathe / drill / milling machine combo. The tiny watchmaker's lathe I have been using up to now is not really big enough for RepRap parts. This should be just about right.



A combo like this is a bit of a compromise and only recommended if, like me, you have limited space. It gives me a lathe, pillar drill and milling machine in a small footprint.

I also bought accessories with my own money, which came to about another £300 :-

• Cutting tools - essential.
• Compound cross slide - for cutting tapers.
• Drill vice - to hold things on the cross slide when milling or drilling.
• Tailstock chuck - to drill down the axis of round things.
• 4 Jaw chuck - for turning square and irregular shapes.
• Milling chuck and collet set - to hold milling bits.
• Wiggler - for finding centres and edges when milling and drilling.
• Die holder - for tapping threads.
• Headstock centre - for turning between centres.

I have also made a couple of accessories with HydraRaptor. The first is very simple: a t-slot cleaner for removing swarf from the cross slide's t-slots.



That saved me about £2.80.

The second object is the biggest thing I have RepRapped so far. It is a cover to go over the chuck to make it easier to turn by hand when tapping. It took over 7 hours to build and weighs 77g.





Here it is installed :-



I haven't used it yet but it feels like it should work well.

Sky Hook

I have found that the most convenient way to provide the filament feed is to throw the whole reel into a large hanging basket and suspend it over the machine with a ball bearing. The machine pulls the filament from the centre of the coil through a hole in the bottom of the basket. As it does this the basket rotates to prevent the filament being twisted.

When the basket contains a full 5lb or 2Kg coil then it does take some force to pull the filament from under the weight of it. Since I sharpened and angled my drive screw and moved to an HDPE filament guide I have not had problems with grip, so this works flawlessly.

I have even started stacking the baskets two deep to save on storage space for different colours of plastic. The top filament can be used simply by passing it through the centre of the lower basket. Obviously only one can be used at a time.



It was easy to attach a frame over HydraRaptor but harder to do over a Darwin. I decided to attach it to the ceiling instead with a "Sky Hook", as suggested by Adrian Bowyer here.



I designed a ceiling mount to hold a skate bearing. These seem to be the cheapest ball bearings to buy. My first idea was to put an M8 bolt through the bearing and attach a plastic hook, but I didn't have any bolts long enough, so I made some plastic parts instead.



The barbs just go through the centre of the bearing, but only when they are twisted over each other.



More by good luck than design, but that means that they can't be pulled out because they pull towards each other and meet in the middle before they can clear the M8 hole.

Just to make sure I made a small locking piece which slots in afterwards to keep the barbs fully splayed.



The bearing then drops into the housing and is held in place by gravity and the ceiling.



The eye and barbs are tensioned along their strong direction, so can be quite thin, but the housing is stressed in the direction where de-lamination can occur, so I made it 4mm thick. It would be tragic if it gave way and dropped a few Kg of plastic onto the machine from a height, so I tested it with a lot more weight to get some confidence.



These 13 wine bottles weigh 16.5Kg, which is 8 times more than the plastic I intend to suspend. It held up for 24 hours with no sign of stress to the parts. Using plastic ties with barbs on the end could be a useful technique for making RepRappable fasteners.

When I came to mount it on the ceiling I realised that the three screw holes were too far apart to all screw into the ceiling joists, which are only 1.25" wide, so I made a two lug version. I made this with 50% fill rather than 25% to ensure it was as strong as the three lug version.



Here you can see a trick I did to get support for the overhanging lip. I just put a one layer thick diaphragm across the hole and cut it out with a penknife afterwards.



Here it is installed : -

Black Heart

I made this tiny heart shaped box as a little gift for my wife's birthday.



Being such a simple shape, with no extruder off moves, it came out perfect, just like my wife.

Pot black

Having tried green ABS and found it a bit disappointing, I had a go with black ABS and was even more disappointed. I got it to try and make objects a bit more aesthetically pleasing but it was even harder to get working than green and has aesthetic problems as well.

The temperatures seem to be the same as those for green, i.e. higher than I have used for plain, but it is harder to get it to stick to the raft and it de-laminates more readily.

To make it stick I had to make the first layer a bit lower than normal. With plain ABS I can have it at the normal layer height above the raft (filament diameter * 0.8) but with HDPE and green ABS I had dropped it 0.1mm. With black I had to drop it 0.15mm as 0.1mm does not stick enough and 0.2mm sticks too much. 0.05mm makes all the difference and has about the same effect as changing the temperature by 10°C.

Another problem is that the extruded filament is not smooth. Close examination reveals that it has small craters in the surface where it has out gassed. It is particularly noticeable when laying the thick filament for the first layer of the raft.



It could be the effect of water absorption but, as all my ABS is stored in the same room, I think it is more likely a volatile component of the black dye. Another effect is that if the filament is stretched while molten, so that it is drawn into a fine thread, then it looks like a string of beads. I think that is an indication the black dye does not mix well with the ABS.

Fortunately, for some reason I don't understand the crater effect is less noticeable when making objects.



These are Darwin y-belt-clamps, a nice small part good for a quick test. The small one is made with 0.3mm filament and shrunk by 3/5. As you can see it is far less shiny. All I can think is that is related to the fact the filament is being stretched more.

Another downside of coloured ABS is that ABS turns white if it is stressed. This shows up far more when it is coloured and particularly with black. Because the base of the object is weakly welded to the raft then it gets bruised when it is peeled off.

This is the bottom of another screw topped pot.



As you can see it has white highlights where the welds to the raft have been broken. One way of fixing it is to wave a hot air gun over it to relax the stress points. That also flattened the base, which was a little convex due to warping.



I expect rubbing it with a little solvent like MEK would also solve the problem.

I now have a little family of pots!



I would not recommend coloured ABS as the dye introduces more variables and generally seems detrimental to strength and aesthetics.

Brassed off

My first attempt at an extruder had stainless steel bearings and a stainless steel drive shaft, more by accident than anything else. I wondered at the time how the bearings would last compared to the recommended brass ones. Obviously stainless steel is harder than brass, but brass should have less friction, so less wear.

The first drive shaft got retired because the bearing lands were off centre. At the end of its life the bearings and lands were still in good condition.



I ran it from 10/07 to 01/08 but up to that point all I had made was lots of HDPE test shapes.

I replaced it with a plain steel shaft that I bought from BitFromBytes. That had the big advantage of being solder-able.

It worked well for a long time but eventually the bottom land on the shaft wore down so much that the pump halves closed together when using undersized filament (2.7mm).



The bottom land has worn down from 3mm to 2mm. The bearings show a little wear but still have some life left in them. This is after running 5lbs of ABS through the extruder.



In the last few weeks I replaced the shaft with a new zinc steel one and switched to brass bearings in an ABS extruder with HDPE filament guide. That worked well until I noticed the pump halves closed together again. When I opened it up I found that the brass bearings had rotated in the ABS, but they had also worn down a lot, considering the short time I had used them.



The drive shaft lands are still fine though.



So it would appear that the best combination is stainless steel bearings and a stainless steel shaft, but I would have to find another way of attaching the nut.

Most metal bearings I have recovered from old equipment are bronze. I don't know how that compares to brass but it seems to be the thing to use.

Maybe it is time to look at ball bearings and an offset shaft like Ian Adkins' design.

Brain dump

I have added a page to the new Reprap Builder's wiki recording all I know about the original MK2 extruder. I make no apologies for including lots of links back to this blog and recycling some photos, but there are also many new ones.

Although the design has moved on, I have stuck with the original and tweaked it to fix the problems I have encountered. I don't think any of the later, more complex designs have better performance, except perhaps the anti-ooze version. That seemed like a nice idea but rapidly got too complex with a double nozzle and two heaters plus some tricky machining. I think instead stringing can be mitigated to a large extent by increasing the speed of moves between extrusions paths. I am hoping to go from 32mm/s on HydraRaptor to 150mm/s on Darwin. Also I think reversing the extruder motor a fixed amount measured by the shaft encoder, plus Enrique's oozebane and comb modules in Skeinforge should help a lot.