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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: Working with large diameter stock
18/04/2016 16:59:58

There is nothing to stop you from grooving as deep as you are comfortable with using your parting tool and finishing off with a hacksaw. Flip the part and face the sawn side to give the required thickness. Just leave an allowance for the final facing operation.


Thread: Jumpin' Gibs
13/04/2016 18:52:28

My lathe cross slide gib is dowelled as others have suggested. Smart and Brown original design. Dowels are about 2.5mm.


Thread: Workshop wiring question
13/04/2016 18:45:41

Any use of electricity in your house will result in a current in the neutral wire. It only needs a small resistance in this cable for a voltage to show up between the earth's zero and the neutral. V=IR applies. This small voltage is able to produce a current in excess of the RCD tripping current when the neutral is connected to earth (low resistance). This small current flowing through the earth cable means the current in the live is different from the current in the neutral so the RCD trips. Avoid cutting the earth and neutral at the same time and there should be no problem.

Since you often share a neutral with neighbours their use of electricity means that even switching off all items in your house may not stop this nuisance tripping. As suggested earlier switching off all power with the double pole switch that isolates the live and the neutral at the consumer unit is the safest thing to do anyway.


Thread: Special ER Collets
07/04/2016 18:35:54

My 7-6mm ER32 collet has a larger diameter for the back half of its bore as do all the smaller ones in my set. This does not cause these collets to grip out of parallel. This implies that it would cause no problem to hold anything with just half the length of any ER32 collet's bore.


Thread: Millling clamps
06/04/2016 19:13:41

I was asked if I wanted to have a drive/ride, I declined the offer.


06/04/2016 10:36:30

Windy, did you see the Warhorse monowheel at Elvington? I have made a lot of the parts for it.


Thread: Fuel pipe
04/04/2016 23:18:41

If you have suitable pipe you could fill it with solder then bend it. Heat to remove the solder after bending.


Thread: How many Methods for Squaring workpieces on Mill ?
03/04/2016 14:15:16

If your fixed vice jaw is set up parallel to the X axis then you can mount the workpiece in the vice with a machined face against the fixed jaw and the face you want to be square to it overhanging the jaws to the left or right. You can then machine that overhanging face by moving the Y axis.

If you want to machine a part without a vice you can clamp it to the machine with some scrap underneath it. As you machine each edge you add and remove clamps to keep the part from moving while each successive edge is cleared for machining.

If you are using a vice and want to hold a non parallel workpiece use of round bars or ball bearings between the moving jaw and the workpiece can be useful.


Thread: Automotive Automatic Gearbox
01/04/2016 09:06:33

Cars with a torque converter do not have a clutch for neutral, there is always a bit of drag from the torque convertor so that the driver has to use the brake to stop the vehicle from creeping along if in drive or reverse with the engine idling. There is enough drag to hold against moderate inclines on the road.

Variomatic gearboxes are in constant drive, they use variable pulleys to change the pulley ratios so there are no disengaged points with that type of automatic gearbox.

The advent of engine management computers in cars brought with them the ability to control automatic gearboxes from them. The old style of Borg Warner gearbox that used hydraulic oil pressures in lots of small pipe runs and galleries in the gearbox to change gear were replaced with solenoid operated brake bands. Ford use 4 solenoids, one of them locks the torque converter input to output to get rid of the small percentage of loss often associated with automatic gearboxes. This solenoid only operates when the engine speed is reasonably steady and the engine is up to temperature but can be noticed operating as the engine rpm can be seen to drop up to 500rpm when it operates. The other three solenoids being operated by the engine management computer can be set to operate so that there is the best change from one gear to the other with minimal time out of drive and gear changes being done when torque in one gear matches torgue in the next gear to give a smooth change. It also allows the gearbox to be put into sport mode where gear changes happen at higher revs.

There are still some losses with torque converters that have prompted manufacturers to chose twin clutch systems over Borg Warner types. Since these are also using the engine management system to operate the gearbox they will also minimalise the time the gearbox is disengaged but since there is some drag with clutches before full engagement they may have one clutch being overdriven when the other is underdriven to minimalise the time the drive is disengaged.

There must be some time when the gearbox drive is disengaged between gear selections to avoid a mechanical lock up. It can be too small to notice and under normal circumstances of a car travelling along a road you would not notice this.


Thread: Calling all Advocates of the "Lammas" 3 way toolpost...
31/03/2016 14:52:59

My compound slide came off when I added CNC to my lathe. It became redundant and just complicated things if left in place. I never noticed if there was a change in rigidity.


Thread: Bedway vee angle
30/03/2016 12:01:45

I have been considering making a positionable home/limit switch for a lathe with CNC. It needs to move because the difference in the safe stop position between spindle collets and a 3 jaw chuck is significant. In my case the near edge of the bed is where the angle is, the top and far side of the way are horizontal and vertical. This sort of design will save the need to accurately measure the angle then reproduce it in the design. The clamping load for a switch positioning block should be much lower than that needed for a mechanical stop so al. alloy and brass are suitable materials and I will not worry about marking the ways.


Thread: Mini-lathe question
28/03/2016 19:36:27

I've seen a figure of 1/64" deflection per inch of straight leg from finger pressure.


Thread: Electronic Artisans ELS Article
28/03/2016 13:15:57

Ajohnw said "I'd be surprised if some one coded a system that just said the spindle is running at this speed so cut the thread and forget it."

That is exactly what Mach3 running through a Smooth Stepper does. If you stop the spindle when the thread is being cut the motion continues to the end of the thread before retracting for return to the start. There may be a difference when using other set-ups but since the index pulse is picked up and sent back to Mach3 by the Smooth Stepper I suspect it is the same with the parallel port.


28/03/2016 09:15:30

Ian, I missed answering you last question. If your spindle slows when cutting the thread you describe then you would need a multi-line encoder system that responds constantly to the encoder input.


28/03/2016 09:10:16

Ian, the slowing down you refer to is the reason single pulse timing does not work for some people. A system using a single pulse, such as Mach3, uses the time between two pulses to calculate the rpm of the spindle. It then calculates the feed rate required for the cutting of the required thread pitch. If the spindle slows when cutting starts the system does not detect this soon enough so the pitch of the thread is longer than it should be. If your spindle kept a constant rpm whether cutting or not then a single pulse per rev will work fine. I think with Mach3 that once the travel speed is set it is not varied until the next code block which is the retract operation of the tool. That is why you get a result like the one in an earlier photo where the pitch stretches after a time as a slowly slowing spindle speed is not detected and acted on. The systems that use a multi line encoder and constantly respond to the input from the encoder should have much more accurate pitch control. I will not say perfect because there will always be some control lag but it should be so low that it is either undetectable or competely acceptable.

The discussion has veered towards how good speed control can be with a vfd. This is because single pulse threading needs this good speed control and so makes either ELS or Mach3 useable for threading in more situations such as large diameters or long lengths of thread where the spindle is more likely to slow down.


Thread: Turntable truck bearing
26/03/2016 22:03:27

Just search for turntable bearing online. Lots of hits, chose the size and load you want.


Thread: Synchronising A lathe Spindle with a CNC milli spindle.
24/03/2016 08:55:15

As I understand the set up the duality lathe can have a harmonic drive to act as a fourth axis. A thread is a helical groove and what you want to do is helical milling. Do you have the 4th axis option? It will allow you to do what you want quite easily, maybe not as fast as you want.


Thread: Sharpening gear cutters
24/03/2016 08:36:45

I have seen cold saw blades that have been repeatedly sharpened using a blade in the gullet to index the rotation from tooth to tooth. After repeated sharpening like this the blade gradually goes out of round and becomes more egg shaped as the process multiplies any small error in the original blade. Original manufacturers of industrial blades (and now some third parties) use proper indexing fixtures to sharpen the teeth to keep the blades circular. Current cost for resharpening a Ø350mm blade is about £10.50 +vat. This is based on a batch size of 40, we use them on stainless steel so get through a lot. It is far cheaper though than regularly replacing them. Some have been sharpened so many times they are down to about Ø200mm. At this size they are only good for small stock.

Used in one of these **LINK**


Thread: Electronic Artisans ELS Article
23/03/2016 13:47:59

I gave the ELS serious consideration for a while. In the end I went for Mach3 running on an old slow laptop driving a Smooth Stepper via USB since I had an available laptop. If you are using Mach3 in Manual Direct Input (MDI) mode then the limitation of short CNC programs only with an unlicensed copy of Mach3 is no handicap. I also have no problem with the single pulse per revolution using a VFD driven 3 phase motor and with the lathe in back-gear. I do not need to run my machine as fast as possible since it is a hobby not a business for me. Running like that there is no perceptible change in speed of the spindle when the tool engages the workpiece even with heavy cuts.

The CNC option gives a lot more flexibility than the ELS and there are easy work-arounds for the length of program limit if you do not want to spend money on a Mach3 license. Lots of experienced people can help with Mach3 if there is a problem. ELS may be harder to troubleshoot, but that is just a suspicion.

Finally I was using Mach3 on my mill so knew what would be involved in setting it up and using it on a lathe would involve.


Thread: Snapping taps
23/03/2016 13:30:14

British Standard BS3643 part 1has a table for metric thread engagement. The table has short, normal and long columns against rows which have a range of diameters and pitches. For an M2 x 0.4 thread short engagement is up to and including 1mm long, that is 2.5 pitches. M3 x 0.5 short engagement is up to and including 1.5mm, that is 3 pitches. This, presumably acceptable, short engagement matches Andrew's post regarding only 3 pitches taking the load. Long thread engagements for these two threads are over 3mm and over 4.5mm respectively. Anything between the long and short values is classed as normal engagement. I think the load and materials involved would determine which engagement would be specified if you were doing a drawing for someone else to follow.

The usual guide of one diameter of thread engagement does not always fall into the normal range in this table, for fine pitches one diameter can be classed as long engagement but it is never a short engagement even for coarse pitches.


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