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Member postings for Ian P

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

Thread: Stripped the drive belt on my Chinese Mini lathe
02/09/2019 15:25:55
Posted by Jim Dalton 1 on 02/09/2019 14:12:35:

Thanks all. I don't think the motor actually stalled. I'm having trouble trying to upload a photo of the belt, bit suffice to say that almost all of the teeth are stripped clean off!

Hard to imagine why so many of the teeth have been removed. I am not conversant with that lathe but its only the driving (motor) sprocket that can do the actual stripping, the driven sprocket has no power (other than inertia) to impart any shearing force on the belt teeth. My expectation would be that once a continuous group of teeth have been removed the motor sprocket would not be able to impart any significant force in section as it would just slip.

I can imagine that if the motor was running and the chuck was stationary (because of some stripped teeth) and the chuck was turned by hand bringing the first good tooth into play, it would most likely get sheared (snatched) off.

Timing belt drive is very robust and reliable technology. My money would be on either a poor quality belt or possibly the wrong pitch belt was fitted in error, some metric and imperial pitches look almost identical, also there are belts and sprockets that have different tooth forms (for low backlash, power transmission etc).

Ian P

Thread: help with gear calculations
02/09/2019 13:21:09
Posted by Andrew Johnston on 30/05/2019 17:06:02:

The results for the rack definitely seem to indicate 14DP. <snip>

The pinion doesn't seem to be that worn, not sure I'd bother replacing it at this stage, if it works.

Andrew

Being a bodger (me not Andrew) I would agree that the pinion is quite usable, it may be that it could be shimmed so that it engages more closely with the rack but I think the biggest improvement you could do is to adjust the pinion position axially so that the unworn part engages the rack.

Without knowing the bearing or handwheel arrangement its hard to know whether its feasible but its worth investigating.

Ian P

Thread: Any idea where to buy a square file 1/4" x 1/4"??
29/08/2019 12:45:14
Posted by Gary Wooding on 29/08/2019 12:25:14:

+1 for a 3-square file - it makes sharper corners.

That not really true all the time. I have square and rectangular hand files with sharper corners than all the triangular files that I have.

It only in theory that triangular are better for square holes.

Ian P

Thread: Help milling an angle
28/08/2019 11:04:57

Clamping material to the bed IS the better way.

Unless the job can overhang the edge of the table (and be reachable by the cutter) you will need packing underneath your workpiece.

Ian P

Now I know how long it take me to type compared with others

Edited By Ian P on 28/08/2019 11:06:41

Thread: Current leakage om CNC
25/08/2019 11:53:40

Posted by fizzy on 24/08/2019 17:11:59:

If I touch the inside of my wrist against my cnc bed I get a highly unpleasant shock. Ive experienced the same sensation with laptop computers but given that there are just 3 stepper motors and a drive motor I wasnt expecting this to occur. I tested the bed to earth and got 120V @ 5 uamps so virtually no current to speak of. Is there anything I can easily do (other than not touching it) to reduce this? Its all on wheels on a concrete floor. Thanks

Posted by fizzy on 24/08/2019

its a chinese set up but the plug has earth. I connected the bed to the trolley, not realy n earth but makes part of the circuit. I dont think there is a workshop wiring fault as it is installed to Iee regs.

Posted by fizzy on 25/08/2019 09:29:13:P

Indeed the stepper motors are under 40v but the spindle motor is 110v. I have a new, unopened motor somewhere so I will swat it out and retest. Thanks all.

About twelve replies so far, some absolutely on target and contain warning of serious risk, some others are irrelevant. To be fair to some of the less useful repliers, the information Fizzy gave is somewhat fuzzy.

Initially he said he measured 120V to earth. The meter will have two probes, one we know was on the metalwork of the machine, but what 'earth' was the other connected to?

Stepper motor and spindle motor voltages, concrete floor, rubber tyres, wheels, Chinese made is all irrelevant!

Unless this machine is of double insulated construction (which is very unlikely) then there should be continuity between the machine metalwork and the earth pin on the end of its mains lead. If there is low ohms continuity then the fault lies in the workshop wiring.

Fizzy, you say connecting bed to trolley form part of the circuit, I hope not! What circuit would that be anyway?

Absolutely no point in swapping motors whatsoever, test the earth wiring and connections first

Ian P

Thread: Meddings Driltru Handwheel (Star Wheel) Stiff
23/08/2019 15:12:22

There are a multitude of materials that a bearing bush could be made from. Nylon would be an unusual choice for this application and HDPE even more so. If Meddings wanted to specifically use a polymer bush they would have been best served by consulting Igus (or just choosing one out of the Igus range).

I know of a company that converted a Porsche 911 to full racing specification and took great pride in showing the complete set of high precision nylon parts they had machined for all the suspension. The first track outing was a disaster as the suspension virtually locked up in the wet conditions!

Ian P

Thread: What are 'spring' collets?
23/08/2019 09:54:06
Posted by Michael Gilligan on 23/08/2019 09:47:53:
Posted by Ian P on 23/08/2019 09:42:14:

...

Nowhere does it mention finger collets though so I'm no wiser on that score.

.

The splits in a 'spring collet' divide it into 'fingers'

MichaelG.

I always regarded the individual sections as 'Tines'.

ER collets do not really have Tines though (as the finger is attached at both ends)

Ian P

23/08/2019 09:42:14

The Rotagrip document that Michael gave a link to does contain some information about spring collets. I've not quite worked out what differentiates them from outwardly identical but non spring versions of the same collet.

Nowhere does it mention finger collets though so I'm no wiser on that score.

Ian P

21/08/2019 21:10:55

I have always wondered what people were referring to when they mention spring or finger varieties of collets.

I just Googled 'what are spring collets?' and the first definition from Google itself is this,

Spring collets are perishable tools for fixing a workpiece at the processing, or fixing cutting tools, and used as some parts of a machine or a conveyance machine. ... On the other hand, when we use spring collets, a workpiece is clamped as wrapping in with the number of flexing slot of the collet.

So now I know!

Not that I am any wiser

Ian P

Thread: Need a lot of help from you good people
19/08/2019 17:06:35

As Dave said. electric motors are tough, if the loco was working before then presumably it can be serviced/repaired/titivated or whatever, I would certainly try and get is up an running before thinking of a completely new drive system.

My guess on the small motor is that it an air pump or small compressor for an air horn.

Ian P

Thread: Home Workshop Site
19/08/2019 17:00:29

I was aware that the site had not been updated for a few days but thought that Adam might be on holiday. If you are in contact with him please pass on regards and hope for a speedy recovery

Ian P

Thread: 4 jaw chuck axial allignment
19/08/2019 10:48:31
Posted by Pete Rimmer on 19/08/2019 08:28:09:

What are you using as a gauge? Simply touching two opposing jaws together and observing the light gap should tell you if they are parallel or not.

Two jaws might pass that test and be parallel to a 1 micron in 10 meters, but they may not be parallel to the lathe axis!sad

Apart from using the toolpost grinder method to true up the jaws, consider doing each jaw individually with a diamond file.

I have dramatically improved two different SC three jar chuck using little more than a diamond file and a bright light source. Since your chuck has independent jaws it would only be a few minutes work to touch up each jaw tip,.

Start off by checking each jaw (out of the chuck) with a set square, that will show any gross error which a diamond file will quickly correct. Once all the jaws are somewhere near they can be checked in the clamped position with a suitable diameter piece of ground test bar or even a length of silver steel.

Its a bit fiddly but an additional check you can do is to wrap a single layer of aluminium cooking foil around the test bar than tighten the jaws on it. You can then see if the whole length of the jaw tip is applying equal pressure.

Ian P

Thread: What Did You Do Today 2019
12/08/2019 16:46:49
Posted by Michael Gilligan on 12/08/2019 10:59:59:
Posted by Martin Kyte on 12/08/2019 10:38:53:

Is ensuring that the cheap bit (psu) breaks rather than the expensive bit (mother board) really bad design?

.

dont know

Not sure that I understand the question, Martin

What I wrote was: "... MagSafe was a great idea, poorly executed."

and I stand by that opinion.

MichaelG.

I understand the question, the simple answer is that it is bad design.

In principle having the part that that is likely to fail, be one that is easy and cheap to replace is good practice, the aim really should be for the whole product to have the same life expectancy. Like may other people here I hate the throw away and buy new that seems to be so prevalent nowadays.

The cost difference between the PSU and the motherboard is not very relevant, its the marketing department that determines the two prices to the consumer and the cost is probably only loosely related to the cost of the item to the manufacturer. What is wrong with the product is that its not designed to be repaired by just replacing a broken connector.

I am hoping that the throw away attitude in society has peaked and that there is an increasing acceptance that its beneficial to ourselves and the planet if we look after our purchases and appreciate them for longer than we do at present.

Ian P

Thread: Flat bottom hole 3/16 o/d
11/08/2019 21:12:04

I have just realised what it was about this thread that had unsettled my tiny brain. I have followed it from the start hoping to find out what engine had a piston 3/16" diameter (I thought a Mamod would be larger than that).

The unsettling bit was trying to get my head round a hole with an 'outside' diameter of 3/16". All the holes I have come across have an inside diameter!wink 2

Ian P

(As to the hole in question, for me its a long series slot drill to clean up after normal drill, or investigate why the hole needs a flat bottom and whether it can be eliminated.)

Thread: Dam Solution?
07/08/2019 00:12:05
Posted by mark costello 1 on 06/08/2019 23:53:55:

Water being discharged from a pipe gave Me the idea of, why not have a generator hooked up to supply electricity to run other pumps? Might help on remote locations. Lights to work at night, cook meals etc....

What you are suggesting is a sort of hydro-electric system, flowing water turning an impeller attached to a generator (well used and understood technology), however there are losses involved in generators and motors so better to use the discharging water to drive an impeller directly coupled connected to a pump. That pump will produce a flow of water from its output so that might as well be harnessed to drive another pump.... ad infinitum...

Do you realise that you have stumbled on to perpetual motionwink

Ian P

Thread: Adjustable 3-jaw chuck designs
06/08/2019 14:38:31
Posted by old mart on 06/08/2019 13:57:07:

Those people who are worried about the possibility of the chuck moving when only the bolts are holding it to the backplate are rarely concerned when using a milling machine with no register at all and 100% interrupted cuts.

I second that.

The main reason for a close fitting register is to ensure the chuck body is concentric. If the chuck is a high quality one then the concentricity of what it is gripping will be as the manufacturer specified and stated on its test certificate.

Having the body concentric also ensures it will be in balance which matters especially at high spindle speeds.

With a slack register and oversize boltholes, one could set up the chuck holding a test peice and indicator, at that same diameter even a bad chuck might grip more accurately than a good one on a tight register, but there is no saying that it will be as good at other gripped diameters.

If the bolts holding the chuck to the backplate are correctly tight then I doubt and cutting force it will encounter would cause and movement.

Ian P

Thread: Serious question, What is a Mini Lathe?
05/08/2019 21:47:27

In a recent posting on this forum regarding the use of a mini lathe the writer mentioned using an ER32 collet. Whilst the ER32 system is not a massive, its nearer the larger end of the ER range.

It set me thinking on what defines a mini lathe, smaller than a 4.5" Myford maybe?

Ian P

Thread: DIY magnetic DRO
05/08/2019 20:37:03

Main thing with machining plastics is to have sharp cutters, razor sharp new ones if possible. Too high a speed in conjunction with dull cutters, or cutters that do not clear the chips quick enough will cause heating and melting of some plastics.

I dont think I have ever milled nylon but I dont like using in the lathe, it produces stringy swarf which can get wrapped round the tool and job, Acetal by comparison is very easy to machine. Last week using a new long series 12mm 2 flute endmill I cut 100mm square holes in 60mm thick Delrin by plunging full depth before moving X and Y in one pass, then a finishing cut to size.

I am impressed with your DRO project and I will definitely by doing the same once I clear my current backlog of jobs.

Ian P

Thread: Tolerance for needle bearings?
03/08/2019 11:09:33

I wonder whether the problem is the threaded rod rather than the rollers.

18mm diameter seems quite large and need quite a lot of torque to rotate it, I presume the diameter was chosen to avoid buckling.

I would have thought a 12mm diameter screw would be more than adequate if its is in tension. It could be driven from the bottom but the thrust load on the screw would have to be taken at the top (so the screwed rod was in tension) and have a decent thrust race.

Ian P

Thread: Laser cut plates
02/08/2019 13:41:13
Posted by ega on 01/08/2019 14:45:01:

Paul Lousick:

Thank you for the explanation.

I suppose I had in mind that it might be possible (if not economic) to run the laser using some suitable cheap material to produce a result which could be checked by the customer; all being well, the real job could then proceed.

I have had many parts made by laser and waterjet cutting and every one was correct and exactly to the drawing I provided (a DXF file). The only ones that were not suitable for use were ones that I had made a mistake on the drawing.

Basically there is no need to make a sample or test cut because the part will what you ordered. Any checking needs to be done before the part is cut.

Ian P

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