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Member postings for blowlamp

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

Thread: Mistakes in Van Rennes article
31/10/2010 11:31:23
It's also a good reason to use a CAD system to generate your drawings that are preferably auto-dimensioned as well.
 
Perhaps the original DXF files could then be made available on this site, which would allow easy corrections  and modifications to be made and distributed.
 
It might also be possible to take original, but basic 2D drawings and let them be updated to 3D solid models by members here and resubmitted for the benefit of us all.
 
Martin.
Thread: Hints and tips
30/10/2010 23:41:09
It works identically to conventional feedscrew dials. As long as you allow for the backlash by winding back a little too far before applying the cut it works perfectly.
 
Martin.
30/10/2010 23:19:21
I recently fitted my Clarke CL300 lathe with a DRO kit from Arceurotrade.

For those unfamiliar with them, these readouts fit directly to the feedsrews of the top slide and cross slide so don't measure actual movement of the axis, but as the provided screws are accurate, the system works well.

They only have 3 buttons, which are, On/Off, Zero and inch/mm and very little in the way of instructions on how to use them, but they do read to 0.001mm!

This could be another one of my "well that's obvious" tips, but I messed about for a day or two and you never know who else is out there that can't see the wood for the trees.

Anyway, to my tip:
 
Take a light cut along your workpiece and carefully measure the diameter. Move the carriage clear of the job and zero the cross slide DRO. Use the DRO to then wind the slide forward a distance equivalent to exactly half the distance you've just measured (the radius).

Press Zero again and you're done!
 
All readings from now on will be of the radius of the part  (ignore the minus sign), which I find much less confusing than zeroing at say 10mm diameter and having the readout display 1.375mm once I've reached 7.25mm diameter.
 
I find I'm using my vernier and micrometer much less after fitting this kit as it really is accurate - far better than I expected.
 
Martin.
Thread: MEW-169 Tool-post Grinder Article
30/10/2010 01:00:25
Steve.
If you're grinding in the conventional way, that is, by the non-climb method, then the backlash is automatically removed as soon as the work head is powered up and turning the job.
Think of how all the backlash becomes irrelevant from the screwcutting train on a lathe when threading.
 
Using a climb grinding technique requires the workhead drive motor to actually function as a brake, because the workpiece will tend to be driven by the wheel and isn't ideal.
 
Martin. 
Thread: Hints and tips
28/10/2010 14:29:18
Any of you struggle to clean your files?
I've never been really pleased with using a File Card to clean them as it never seems to completely remove all the pinning.
 
The best way I've found is to rub a piece of brass bar across the file until it forms to the shape of the teeth. At this point, it can be used to remove all debris quite easily. It always surprises me how much muck gets embedded in there.
 
Martin
Thread: MEW-169 Tool-post Grinder Article
28/10/2010 13:42:44
Greetings all.
 
If I can relate my experience with surface grinding, using a horizontal spindle machine, it might be of some help to those that are new to the process of precision grinding as the principles can be applied for cylindrical grinding too.
 
After doing all the preparatory work such as selecting and dressing the wheel and mounting the job to the table or chuck, comes the actual process of passing the workpiece under the wheel to remove the waste material.
 
Firstly, use a common sense approach to find the point at which the wheel just touches the top of the job, similar to those used for milling etc.
 
Position the workpiece in front of the wheel, with a small gap to allow the workpiece to traverse without passing under the wheel.

When you've done that, apply a roughing downfeed in the order of 0.01mm to 0.02mm and flood with coolant.
 
Start to traverse the workpiece smoothly, left to right at an appropriate speed - and if we're talking about a manual traverse machine here, this usually means about as fast as you can move it!
 
Apply a crossfeed of about 2.0mm at the extremity of table travel, but note that with a wheel rotating in a clockwise direction, any crossfeed applied whilst the work table is moving right to left will be a climb cut and so more likely to grab, particulary if an anti-friction work table is fitted. If the wheel does grab, it can move on its flange mounting or become crushed locally, thus causing defects in the finish.
 
It's quite possible to crossfeed at either or both extremes of travel and depending on how all the above factors are interacting with each other, this may or may not have an impact on surface finish.
 
If conditions are right, you'll get a lovely smooth finish. If things aren't going your way, you could be seeing judder, crossfeed lines, or burning. The first thing you should do here is dress the wheel to open it up and allow it to cut freely again.
 
Check out some of the models and tools at any exhibition and you'll almost certainly see some of these defects. In my opinion it's purely down to unfamiliarity with the grinding process and is not intended as a criticism of the builder.
 
When I started, I found it best have quite a fast table speed, as it helps keep the wheel sharp. Having it too fast will open the wheel up so much that you'll get a very coarse finish on the job. You'll then need to re-dress the wheel and slow the table until you reach a good compromise of finish vs wheel wear.
 
Bear in mind that varying the wheel speed whilst keeping the table speed the same can also be done, as the important factor is the ratio between wheel speed and work traverse speed, because this ratio determines chip size and tooth (wheel grit) load.
 
As an example:- With the wheel locked in a stationary position with only the workpiece moving past the wheel, would result in a chip of size equal to the length of the job multiplied by the depth of cut. This is an impossibly large tooth load and would break down the wheel quickly. Reversing this scenario should highlight the other extreme, that being, tiny chip equals tiny tooth load which in turn equals a soon to be blunt wheel (frequent dressing).
 
Finding the right balance of the above is the key to good grinding.
 
 
Martin.
 
27/10/2010 18:02:19
Chris.
Before I continue with a further reply, could you just tell me whether you accept that with both wheel and workpiece rotating in the same direction, it equates to the conventional milling analogy and that by reversing the rotation of the workpiece, the analogy changes to that of climb milling?
 
I'm intrigued by what you mean when you say it's a "Red Herring". Perhaps you could expand on that also, please?
 
Martin.
27/10/2010 00:35:56
Chris.
I thought it was you that mentioned red herrings? My reply was to that comment only.
 
I have to disagree with you about the wheel only seeing the work (move) in one direction though, because if you look at the wheel/work rotation relationship again, you'll see it can't be true.
 
With the wheel spinning at any constant speed and direction and then presented to the outer periphery of a workpiece spinning in the same direction as the wheel, the chip will begin life at zero thickness and by the time it severs from the job will be equal in thickness to the cutting depth of the wheel.
 
If you now reverse the direction of rotation of the workpiece only, then the chip thickness starts equal to wheel cutting depth and ends at zero thickness. These examples are fully equivalent to conventional milling and climb milling respectively.
 
Martin.
26/10/2010 21:48:40

I can tell you what I know to be important when it comes to precision grinding and getting a good surface finish on materials such as cast iron and mild steel, as can be found on machine tools - so we're talking components like cross slides and spindles etc.

Obviously use the right type of wheel for the material being worked, which usually means silicon carbide for cast iron and aluminium oxide for steel. Use a wheel of correctly sized grit and openness, as well as the right degree of hardness for the job in hand.

In my experience, most people don't do much of the above unless they have to and just use what's already fitted on the machine, but still get acceptable results provided they aren't doing long job runs.

The next thing is to true the wheel to make it round, followed by dressing, to create the right surface texture. It is vital to dress the wheel properly, but unfortunately many folks make the mistake of passing the diamond across the cutting face of the wheel far too slowly. This has the effect of blunting the wheel and leaving it useless for its intended purpose. Evidence of this can be seen by the presence of any or all of the following:- Burning, judder marks and a burnished finish on the job.

Running the wheel too fast and/or the worpiece too slow, has the effect of making the wheel act harder and prone to blunting, in the same way a milling cutter will blunt quickly if spun too fast. Similarly, if the wheel is run too slowly or the workpiece too fast, the grit will be torn from the wheel because the chip load per tooth (per grit) is too high and results in a wheel which won't hold its size, but will cut like a demon as fresh new grit is constantly being exposed.

The art is in getting the right balance between all the above factors so that new grit is exposed as the old grit is torn away as it becomes blunt, ie. chip load increases to the point where the wheel breaks down and so self-sharpens.

If you accept any of this, then far from being a red herring, you can see that the direction of rotation of the workpiece, as well as its speed in relation to the wheel is important, as it is linked to the wheel-speed/work-speed ratio.


Martin.

Edited By blowlamp on 26/10/2010 22:22:55

26/10/2010 12:33:31
I think the reason for the grinding wheel and surface of the workpiece to be moving in opposite relative directions to one another is similar to the reason why climb milling isn't recommended in all circumstances.
 
If the points of contact of both the workpiece and the grinding wheel are moving in the same direction, albeit at different speeds, then you are in effect 'climb grinding', which has the dual action of driving and pulling the job, deeper into the cut. If there is any lack of rigidity within the system then a poor finish is more likely.
 
Martin.
 

Posted by JDEng on 26/10/2010 08:39:15:
Thanks for the welcome Steve!
 
After I had made my post I had a look through various textbooks which I've gathered over the years and they all state that the work and the wheel should be moving in opposite directions at the point of contact but none of them actually give the reason why. Thus they both need to revolve in the same direction if external grinding and in opposite directions if internal grinding.
 
What they do all agree on is that when toolpost grinding you need to achieve the maximum amount of rigidity in the set up if you are to achieve anything like a decent finish.
 
I'm with you Bogs on using a machine; I think you need to take common sense precautions such as covering slideways, cleaning down well after wheel-dressing and at the end of the job etc but at the end of the day they are machine tools for using. I've seen some awful abuse of machinery in industry and it still keeps working - not that I'm condoning that but I do think you've got to keep a balance between practicality and keeping something in cotton wool.
 
By the way has anyone seen the new toolpost grinder by Hemingway Kits?
 
John.

 

Thread: Simpler the Better -what do you use?
22/10/2010 14:09:39
Hansrudolf.
I can't tell you why you're not getting the full window, as it's not something I've experienced.
As for some of your other questions...
...here comes another video 
I have some additional tools, as I'm running ViaCAD Pro v6, but your demo version of ViaCAD 3D/3D v7 has some tools, bug fixes and enhancements that I'll have to wait for, until Pro also gets an update to v7.
 
Go to Menu -> Help -> Tutorials and check out some of the included videos etc, to find out more.
 
I'm by no means an expert at using ViaCAD, but I've managed to do what I need. If you want a tutorial thread, I'd be happy to contribute where I can.
 
Martin.

Edited By blowlamp on 22/10/2010 14:26:30

21/10/2010 10:59:12
Hi Chaps.
I sometimes find it easier and quicker to do a demo video than try to explain a feature.
There is a demo download here. http://www.punchcad.com/demo_form.cfm

And another rather large (13.6mb) video of me doing some holes, etc and forgetting to change the Workplane to correctly orientate the Polygon for use with the CutOut tool.
 
Incidentally, the Hole tool can also do Counterbores and Countersinks of any sensible depths and angles.
 
 
I hope some find it useful.
 
Martin.
20/10/2010 10:47:30
Hi Versaboss.
It probably depends on your definition of Parametric.
Line lengths and angles are easily changed, but not by directly editing any dimensioning you may have entered.
Changing a lines attributes updates the dimensions, rather than the scheme you mention, that changing the dimensions has the effect of updating the lines attributes - if that makes sense!
To try and make it a little clearer, I've included a link to a video I made, that tries to answer some of your questions and shows the switch between 2D and 3D modes.
If it's still not clear, then let me know.
 
Martin.
 
Thread: Tool tips
20/10/2010 09:33:17
I believe the 5 degree figure is from a 1988 copy of Know Your Lathe.
I attach a screenshot of the relevent page.
 
Martin.

19/10/2010 23:51:21
And to cap it all, Boxford say that for plain external turning, the correct tool height is 5 degrees above centre height. Presumably to ensure a positive thrust against the cross slide feedscrew and thus prevent any tendency for the tool to be drawn into the workpiece.
 
Martin
Thread: Simpler the Better -what do you use?
18/10/2010 22:20:35
Just to add a little more meat to the bones of my previous post.
I find that ViaCAD has really good, clean DXF and STL file exports, which makes life so much easier when working with a CAM system (in my case, the mighty CamBam).
If you only want to work in 2D, then 1 click on an icon and all the 3D related stuff is taken offscreen - another click and it's back. Very simple and effective, particularly for newcomers, which I think is what the original poster was looking for.
 
Martin.
18/10/2010 14:26:23
Anyone looking for an easy to use CAD system should cast an eye over the ViaCAD range of products. I've been using ViaCAD Pro for a couple of years now and find it to be exceptional in its drawing and file sharing capabilities.
Rather than me try to list its functions I'll just include a link.  http://www.punchcad.com/full_store.html prices start at less than US $50 or £32.
 
Martin.
Thread: Hints and tips
18/10/2010 11:02:09
Greetings all.
 
Well I don't know how most of you have been using your calculators to convert fractions to decimal, but up until quite recently I've used a pointless and slightly long-winded approach.
 
To use an example of let us say 17/32, I've been dividing 1 by 32 and then multipling by 17 to achieve the answer of 0.53125, which is of course correct... I'm sure some of you are laughing already.
 
However, I 'discovered' that dividing 17 by 32 also gives... 0.53125. So just enter the fraction into your calculator literally as it is written and it works for any fraction, no matter how bizarre, such as 21/89 = 0.23595... or even 89/21 = 4.238095...
 
It's still not obvious to me why I've been doing it this way for so long, because I know that 1/4 = 0.25 and that 1/2 = 0.5 and so would never dream of employing the first method to work out these examples, but then maths never was one of my strengths. The main thing is that it saves a few seconds and slightly reduces the chances of making a mistake in the calculation. 
 
I hope it helps some of you.
 
Martin.
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