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Member postings for Martin Connelly

Here is a list of all the postings Martin Connelly has made in our forums. Click on a thread name to jump to the thread.

Thread: What do i need for my new setup
06/01/2016 18:58:45

A lot of lathes have morse taper spindles but certainly not all. Also morse taper tool holders for a mill do not have a tang, they have a threaded hole for a drawbar. This means that some tooling such as a drill chuck may be used on lathes and mills but are not necessarily easy to remove compared to a tailstock that ejects tools when retracted or spindles with a slot for putting a drift in. This is where the comments about banging on a draw bar or other length of rod comes from. Do not put milling cutters in a drill chuck, the cyclic side loading can loosen the chuck with unhappy consequences. If you have a choice between morse taper and R8 on a mill the cost of tooling to fit it should be something to consider before making a choice.

Martin

Thread: Unwanted Taper on Big End Bolts
06/01/2016 18:40:53

Tony, I have used a centre with collets and chucks as well, I was referring to a discussion here http://www.practicalmachinist.com/vb/south-bend-lathes/turning-between-centers-vs-chuck-130393/

If the centre is not aligned to the spindle axis of rotation it can move the part off the centre of rotation and so cause problems, that was why I was asking if the tailstock alignment had been checked. The original question is under the heading of beginner questions so it seemed to me to be a legitimate query to the op.

Martin

Thread: Rotary Table
06/01/2016 14:59:34

Not quite true Nicholas, see the message at 13:35.

Martin

Thread: What do i need for my new setup
06/01/2016 14:08:32

Ega, maybe that's something to check for then when looking at mills. If it is a morse taper spindle does it have an easy release mechanism?

Martin

Thread: Rotary Table
06/01/2016 13:35:16

Are you planning to put chucks off your lathe on it? This thread rapidly followed the assumption that that is what you will be doing. If not then the answer is possibly whatever fits other criteria such as size, weight, height and cost.

Let us know how you intend to use it and if there are any specific things you have in mind for it or if it is a "need to get at some point item" that you are putting some forward thinking into.

Martin

Thread: Unwanted Taper on Big End Bolts
06/01/2016 13:16:25

There are a lot of people that will take the view that if you are using a collet or chuck you should not also use a centre in the tailstock. Any slight error in the tailstock alignment will introduce a distortion in the bar and result in odd errors such as you are reporting.

As Andrew said you should be moving the saddle and with power feed if you have it.

Have you either bought or made an accurate test bar to check tailstock alignment? How did you align the tailstock or have you ever checked it in any way?

How accurate is the 1/2" diameter of the bar and is the collet an exact match to it. Is the collet and its seat perfectly clean and free of damage?

What rpm are you running at? Carbide inserts work best at high speed and the speed for a diameter like this with carbide inserts may need to be as high as 2000rpm for a good finish. They also need a high feed rate to get the best from them otherwise they can rub since they are relatively blunt compared to a well sharpened and honed piece of HSS.

If you have a plain bar to put a thread on you could turn it between centres. This gives the option to measure the thread and put it back in the lathe with the correct positioning to cut some more depth in the thread. Once again this requires that the tailstock is properly aligned but that can be checked as you start to reduce the bar, it should be parallel after each cut, A steady rest can be used if the bar is going to get a high slenderness ratio as its diameter reduces.

0.1mm cuts on a Ø7.6mm workpiece may be a problem for carbide inserts. The centre of the workpiece will try to move away from the tip and so cut less than at the constrained ends, have you any HSS to use for these finishing cuts? It will be probably be sharper than a carbide insert and the force pushing the workpiece away will probably be lower as a result.

Martin

Thread: What do i need for my new setup
06/01/2016 10:36:44

Consider power feed for the mill. If it is not an option for the one you look at you may soon finding yourself wanting it. It is easier to get a mill you know can have it added in the future without a lot of messing around. Power feed does help with finish as well, it also frees up hands for other things such as brushing away swarf and spraying coolant or wielding a vacuum hose.

As Bazyle said when looking at mills bigger is usually better, you can do small things on a big mill, the other way round does not work. A lot of people have bought the 6x26 (Warco VMC or Chester 626 for example) milling machine and found they need to make a riser for the head to get acceptable clearance. This is just an example of what happens if you get a mill that seems big to someone new to mills.

As Tractor man says DROs make life with a mill much easier. If you buy a mill ask if there is an option to have them fitted at the time of purchase, you do not have to buy it but it will tell you if it is possible to add yourself if required in the future.

Clamping kits and/or vices are something you will need to use the mill as well as some end mills or other cutters.

I would suggest you avoid a morse taper spindle if possible, some may disagree, because of the number of posts I have seen asking for suggestions on removing ones that are stuck. I also think that having to bang away on a drawbar if one is a bit tight to remove does not do a lot for set up when trying to maintain position between tool changes.

Martin

Thread: Lathe tool geometry for threading aluminium
06/01/2016 09:48:51

I agree with Hopper, the backgear is only going to drive the motor train if it is engaged for hand powered threading on my lathe. I would disengage the backgear and leave the drive pulley on the spindle unlocked so the motor was not able to drive the spindle, much safer when a crank handle is sticking out of the back of the spindle and no effort going into manually turning the motor.

Martin

Thread: Recommended material suppliers
05/01/2016 21:40:54

No, Speedy Builder5, he works for a Peterborough engineering company but they have a small workforce embedded in the place I work. He has to buy his materials through the Peterborough purchase department but what we are doing is not a formal setup. He has a regular requirement to supply a short piece of 1/2" diameter phosphor bronze so just wants to cut a piece off a bar with a hacksaw and file it flat on the ends. Almost all the machining done in the place I work is now done on CNC machines and anything else is put out to sub-con. The last manual machining department was closed last year. Add on the £70 an hour labour cost for in house work and you can see why he wants to use an informal system to keep his costs down.

I am buying the 1/2" diameter personally and so keep the larger diameter personally. He has already paid out for the large diameter bar but gets what he wants without any further cost reducing its diameter. I get the large diameter bar for the cost of the small diameter bar. Hope this makes more sense now. 

Martin

Edited By Martin Connelly on 05/01/2016 21:47:20

Thread: Emco Compact 5 Motor Problem
05/01/2016 20:00:00

Can you mount the motor on electrical isolators to see if that stops the fuse from blowing? That would confirm if there is a short to earth from the motor. If you put a low wattage incandescent lamp in series with the motor to restrict the current you will also find out if the fuse is blowing due to an internal short in the motor.

Martin

Thread: Recommended material suppliers
05/01/2016 19:45:09

I've just ordered some pb102 phosphor bronze from Maccmodels. Some one asked me today to turn a 350mm length of 26mm diameter pb102 down to 1/2" diameter. I had to check twice that I had heard him correctly. He has to buy from approved suppliers for his stock material and he asked for 1/2" diameter and got the 26mm at the price for 26mm bar. I said it seemed stupid to throw 3/4 of it away as swarf. We struck a deal instead, I keep the 26mm diameter bar and supply him with two lengths of 200mm x 1/2" which is what I have ordered. It saves him from having to pay for the machining (some bottles of beer in my case) to get the size he wants and I get a nice piece of raw material.

Martin

Thread: Warco BH600G Modifications (clutch, gears, 3 phase)
05/01/2016 18:33:17

Use a pound coin. It is very similar to aluminium bronze and the only part that needs to be in the correct material is the face in contact. There are plenty of forgeries in circulation so if you use one of those you are not breaking any law if you destroy it.

Martin

Thread: Who can regrind a shaper way?
05/01/2016 14:35:37

Any chance of scraping the surfaces yourself? I've never done any myself but I see a lot of posts where people claim it is easy. In this case the hard part is ensuring squareness of the finished surface to an existing surface if there is no adjustment in the machine's design.

Martin

Thread: Thread cutting and Change gears
05/01/2016 14:30:33

They can be used as idlers. Idler gears can be any size but they need to be a size that allows a set-up. If you have pre-owned lathe then there is a possibility you do not have a full set of gears and the duplicates can be used instead of idlers listed on a change gear chart that are missing from what you have.

Martin

Thread: Time for a name change?
05/01/2016 11:56:23

Good call Duncan, CNC is just another tool.

Martin

05/01/2016 11:47:22

Roy, most of my work on my CNC modified Smart and Brown and Rong Fu mill is done without a program. I go into the workshop and switch on the power to the laptops and machines and then do the same sort of thing any manual operator will recognize, set up a workpiece, set up the tooling. Work out the tooling position relative to the workpiece to know how much to move it to get the desired result, check the result as the work progresses. The difference is that I cause the tool to move by instructing the motion through the CNC program manual data input instead of by turning handles. No time spent programming at all for basic machining.

Martin

05/01/2016 11:31:14

There is a halfway point in home CNC between fully manual and fully CNC. I think a lot of home machinists who have CNC will work this way.

I made my machines CNC for times when CNC allows me to do things that are hard or possibly impossible to do without CNC. A lot of the time I use them with MDI (manual data input). There is not a lot of difference between turning a handle 1mm by hand and telling the computer to turn the handle 1mm.

What I get from CNC on the lathe is never having to mess about with change gears anymore. I can cut imperial threads or metric regardless of what gears I have or the leadscrew pitch. I can chose a feed per revolution and if it's not quite right I can try a bit more or a bit less on the next pass or even during the pass if it is long enough. Want to turn a bar down taking a lot of passes or bore out a small hole to a large hole? I can use a wizard and let it do the bulk of the work and take over for the manual input when I approach target dimensions. Recently I was asked to make a bellmouth for a carburetor intake **LINK** . It required an elliptical curve on the inside and a circular curve on the outside. I spent some time working out the maths equation for the coordinates for the cutter to follow then wrote a small program for the lathe. No sitting down with a PC and just putting a DXF into a CAM program. Formed the complete curve inside and out with a 6mm button tool without pausing between start of the curve and the end of the curve.

On the mill I can do a similar thing, use MDI to treat it like a manual machine with input through the keyboard instead of turning handles. Does winding a handle manually from x=100mm to x=200mm take more skill than telling the computer to move the table 100mm from 100mm to 200mm? I can tell the spindle to move down at a rate of 0.05mm per revolution to a specific depth when drilling a hole and tell by the sound and swarf coming off if it should be faster or slower feed. Does it really mean I have less skill than someone who is doing the same thing by winding a handle? I have still chosen the rpm of the spindle to suit the cutting tool the same as anyone working without CNC.

CNC does not de-skill someone, it just changes the skills used for achieve an end product. How much computer power is used to get to the end product will vary from person to person but for what I do it is only a small step away from manual machining. Hobby machining is a very wide spectrum of ability and processes.

Martin

Thread: Stirling Engine : Laura
05/01/2016 10:35:02

Make a stiff card radius gauge to check against if you are going to manually make the radius. It does not need to be a perfect curve as it going to be in the bottom a test tube that is probably not a perfect hemisphere anyway. It just needs to look good in the tube.

Martin

Thread: Warco BH600G Modifications (clutch, gears, 3 phase)
05/01/2016 10:27:01

Screw cutting up to a stop is going to be a case of immovable object trying to stop an irresistible force. Something has to give way and if you are lucky it will be a drive belt slipping. If you are unlucky, which is more than likely, you will strip a gear of some teeth, break a drive key, distort a shaft, damage a mechanism, break your half nuts or the leadscrew. All of these are considered bad and so not something to be taken lightly. Due to the high reduction required to reduce the carriage speed for fine screw cutting it has a lot of force trying to move it along the bed. Even using a handle and turning the shaft by hand you may not be able to feel the resistance of a carriage stop. My lathe has a shear pin in the leadscrew drive for when this happens and it is not the easiest thing to access and replace but it is considerably better than damaging something that is not designed to give under load (bust it once by inattention).

Martin

Thread: Fly Cutting
02/01/2016 23:40:18

The link to the photo clearly shows a ground tipped tool for flycutting. The text refers to cutting a slot with an end mill mounted in a collet. This is not flycutting with an end mill.

Martin

Edited By Martin Connelly on 02/01/2016 23:40:56

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