Here is a list of all the postings Neil Lickfold has made in our forums. Click on a thread name to jump to the thread.
|Thread: Milling cutter damage - what am I doing wrong|
If you are running a high speed steel cutter at 360 rpm , and it can not take a 1 or 2 mm cut, then your machine does not have enough rigidity.
In smaller machines you would be better off using a smaller 8 or 10mm end mill.
8mm and 10mm tungsten carbide cutters are very affordable now days.
You can run a carbide cutter at higher rpms, The most common cause of cutter damage is by swarf getting trapped between the cutter and work piece, Having a high flow of coolant or even an air fog buster onto the milling cutter will dramatically increase tool life.
|Thread: Precision diameters|
The alloy used in high performance model pistons contains 30% silicon among other things and is very low expansion. Typically the liners or cylinders are made of 9-11 % silicon material. Usually what happens is when the engine over heats, the liner and the head expand, making the liner larger than the piston, and it just slows down, it is very rear to see a seizure. Essentially the top 2mm of stroke or so on the setup effective runs dry with no lubrication. These are the highest pressure areas. Small gains in the effective seal have a huge effect on power output and overall efficiency. In one example of tuning, the same timing numbers were used, but made into a square arrangement, so the bore was almost the same as the stroke, the power output gain with this engine with a small change in the piston geometry made a power gain of approx 7% . The new setup makes more power for a longer service time, a lot of the extended life is due to the profile of the piston and making it so that it rocks less in the cylinder. The high performance model diesel engines are the most critical in piston fits, and the best of those engines are now turned on sub micron CNC lathes and sub micron cylindrical grinders. What I can achieve for the glow plug engines, would not make a world class piston fit to the modern racing diesel engines. The glow plug engines are a little bit more forgiving. For general purpose model diesel engine with a regular liner in a case , my set up is fine, but the newer integral liners where the head is part of the barrel, is a very different matter.
Cylindrical grinders are usually far more accurate machine due to the precision of the work head bearing set up, and the very low vibration from the balanced motors. Very accurate head bearings do not spin very fast to maintain their accuracy.
Changing my lathe to the smoother 3phase motor on a VFD has made a very big improvement in surface finish.
One last thing, the tools have to be very sharp , when they are dull , they tend to burnish as they cut, those will not work as well either. If the tool can not take a 0.002mm cut with the oil, it is too dull. The high silicon alloy is so abrasive, that even carbide tooling does not last very long when trimming pistons. So I rough out using carbide and then use the diamond tooling for finishing, usually leaving only about 0.05mm on diameter for the diamond finishing insert.
|Thread: Deckel SO Cutter Grinder|
I really like the D bit grinders, there is so much that can be done with single lip cutters.
If you get the double sided wheels in either diamond or cbn, the you can grind thread cutting tools and the like. Also do bull nose radius cutters( offset corner radius cutters)
I have been looking for one, but they are too expensive even second hand. The cheap import ones are not as good as a Deckel.
|Thread: Precision diameters|
I do not know the Ra values sorry. But I think the reason it works better is that the interference fit, effectively burnishes the piston to the final running fit size. When lapping , you are taking away these peaks and so the piston can not burnish to get the liner specific fit. I think this is why when you run a piston in another liner, it does not run as good as a new piston that was fitted to that liner. I have not found a way to make the lapped ali pistons work.
Hope that helps.
It is a combination of fit for the final position and measure ment. Most model engine liners have a taper of Ø 25um per 10 mm or .0025mm per mm length. So to get the piston to the fitted length if it is 2mm away will require removing .005mm off the diameter. It does take a bit of experience to get it right. If the part has a temperature increase from the turning, you will not make it work, as the size while turning will change.
I have a very good mic with a non rotating barrel and use it like a comparator mic. I am in the process of getting a comparator mic with the dial gauage built in.
The other way of measuring but is very cumbersome , is to use a Vee block and a low pressure finger clock graduated in .001mm increments. But the total range on such instruments is usually about 0.1mm meaning you have to be within 0.06mm of size to even use it. I cannot measure better than about 0.001mm or so. I can certainly get to better than 0.002mm . An error of 0.001 is going to be about 0.4mm on the piston fit position.
Everything has to be degreased and be oil free when measuring. To cut at these small tolerances , I use a mixture of canola oil and about 20-25% crc , for the piston trim I use a positive rake ccmt11 PCD insert. Honing oil is also a very good cutting compound, but is more expensive .
I can fit on my Myford a piston easier and get it right compared to using a standard cnc lathe that has 0.001 resolution. To really be able to make these right requires, sub micron lathes which I do not have access to out here in NZ. These pistons could be lapped to size, but those do not perform as well as ones that have been turned to size. In a mass production set up, these pistons are turned in batches with 0.0005mm or so difference in size and the correct graded piston is then selected to fit that liner.
But this process , will help those who need to achieve 0.002mm size on parts if it needs it.
You need a lot of things to fall into place to get the accuracy that is for sure. You need the temp to be some what controlled, I have a small room built in my garage just for the lathe, with a dehumidifier and a heater for winter. I have my own mix of oil I use on the slideways, it is just 30/40 motor oil with lucas oil stabiliser and some stp oil treatment in it.The lathe bed has been levelled with a precision machine level to get the warp/twist out of it .The standard Starrett ones are not really accurate enough.I brought my own and am very happy with the results. Saddle has been re shimmed to get the better tolerances. Cross slide is adjusted to be quite neat but can me slide by hand, then the screw and nut assembled and correctly aligned. I made a M8x0.5mm pitch screw and nut so that the inches dial now matches the micrometer dial in metric.The down side is the slowness of the cross slide in travelling any distance.Compound slide is adjusted to be just sliding but not binding.I refitted the compound slide as it was, there was a slight taper in it,either wear or like that from new.I only use my Myford lathe for my precision work and thread cutting. All roughing out/blanking out is done on another lathe I have.
I hope others can learn from this , and help them to achieve accuracies that otherwise are not easy to achieve.Even making the M8 fine Pitch thread instead of the course 10 tpi that was in there has been a huge step up in accuracy.
As you can tell, I spent a lot of time setting up the lathe to get it do do what I want.
With my set up, 2 thou on the compound is 0.001mm diameter.
The hardest part of it all was getting the head stock bearing lapped and scraped to run true enough, and then having the end play correct.
I can not run my lathe in the high rpm range otherwise it will start to heat up.
If it is backed off to run at the higher rpm, it will not be running true enough.
Not sure if this has been covered before.
But to get a very precise diameter, I set my compound slide on a 1/2 deg aprox angle.
Then when I am close to the diameter I need, I use the compound slide to make the X movement.
With this set up it then becomes possible to get to micron sizes.
You have to either take some test cuts or use a dti to figure how much each graduation on your cross slide takes off the diameter. Also make sure the cross slide gib is not too loose as well.
I use this method for sizing pistons to F3D (6.5cc race engines) where a difference of 0.003 mm in diameter is either too tight or too loose and worn out.
|Thread: Myford Super 7 Inverter Drive|
I brought an Eric Drive VFD that is programmable for acceleration and deceleration .My motor is a 550w 1440 RPM.
I have a 2 way switch where the original forward reverse switch was. Above the lathe is the control box mounted in a housing box. On there is the main on off for the VFD, and the pot with some numbers representing Hz approximately.This controls the motor speed. The control on the VFD displays the actual HZ .I have the hertz range set from 30 HZ to 60 hertz. That along with the belt changes, I do not need to go into back gear any more.
I have not done it yet, but intend to connect an adjustable micro switch, so that when it gets to the switch the motor stops. I have mine ramping down and breaking, and set that to 0.2 seconds. I also have the start ramping at 0.2 seconds as well. The intention is to use it for cutting internal threads and having it stop at about the right place.Any quicker at stopping,and you risk the Chuck coming undone.
When setting up the VFD there are parameters like the Max motor current etc. When set up ,it still has loads of power even at low RPM's. The only waning is that the motor can get hot if continually run at very low rpm's.In these situations, they recommend adding a small fan to keep the motor cool.So I have my min hz set at 30 as recommended by the place that sold the motor and VFD unit.
My only wish is that I should have gone this way much sooner that is for sure.
|Thread: Myford Capacitor problem?|
My motor had problems back in 2005. I thought it was a cap problem, so took the motor off and to a place to check it out. The man un soldered the cap,tested it and said it was all fine. I took it apart, he looked at the brushes in the switch, although not perfect he said that it still should have been working. I put it all together, he soldered back on the cap, connected some wire and worked fine. He said that sometimes over time, the soldered connection of the wires to the cap need re soldering. I took it all apart as I thought that there was a problem with the centrifugal switch. I was wrong.
It worked faultlessly until 2012, when everything stopped again. This time it was the forward and reverse switch that went. So I retired the motor and put on a 3phase motor with a VFD drive. The motor still works fine, and is sitting on the shelf as a spare for something one day.
|Thread: Types of Boring bar|
There are a new generation of boring bars that have vibration dampening technology. Some have a carbide or some other heavy metal that vibrates and counteracts the vibration from the tool. Another one in the small bar sizes is the Dynamic series from Kyocera, or the Dimple series from Mitsubishi.They make them in steel and carbide shanks. Carbide costs a lot more but has a lot longer diameter to length ratio.
After using the vibration dampened tools, you will not want to use standard tools again.
I have made dampened tools to external turning for tools that needed to have along over hang.
To test the effectiveness of the tool in making it , I tap the side of the tool and if it does not ring, it will be fine.
In the small bars I like the ones with a sort of triangular shape that allows 3 cutting edges instead of the 2.
|Thread: Original maching marks on Myford lathe bed|
My myford has a ground lathe bed, so does a friend's lathe. Mine is a super7 made around 1974.
The only slide that has scraping is the compound slide. Not sure if that was original or done by the previous owner.
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