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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: Parting off on Myford lathes
19/01/2011 10:52:26
Myford drive belts are flexible, but they aren't stretchy - if that is what people are meaning when they say they are elastic.
 
I would still like an explanation as to why this theory doesn't apply to lathes that have geared heads and primary drive belts from the motor.
 
Taking a second cut creates a wider slot and simply gives more room for chip clearance.
 
Martin.

Edited By blowlamp on 19/01/2011 11:02:34

17/01/2011 14:40:13
Those drawings are put together in such a way as to reinforce the argument of the author.
 
To my way of thinking - and this is assuming that both the tool and toolpost are up to the job - then the pivot point should actually be at the front foot of the toolpost on the left, which is almost directly under the tip of the cutting tool.
In that position though, there is so little extension of the tool beyond it's support footprint, that there is practically no opportunity for a rocking movement to happen due to a downward force on the tool.
 
Non of the above helps the assertion of the rear toolpost being stiffer, as the strength of the tee-slot mounts must also called be called into question when evaluating it's merits.
 
Anyone with a Gibralter type toolpost should be able to verify that deflection is minimal when parting-off and thus do so with few problems, provided the groove can be reliably cleared of swarf. If a jam-up still occurs with a Gibralter - but not with the same tool mounted at the rear - then I'm pretty sure it's chip crowding.
 
All the above assumes a lathe in good condition.
 
Martin.
17/01/2011 10:39:19
I'm struggling with some of the logic of the 'elastic' drive belt theory in this thread.
Anyone that's ever tried to stretch one of these belts will know that they've got virtually no give in them at all, let alone be elastic.
They are after all reinforced with various types of cord to prevent this.
 
It also would be interesting to know if this theory for a Myford holds true whilst utilising it's back-gear.
 
I have a geared-head head lathe that is belt driven from the motor and am intrigued to know if the theory predicts that it also will be subject to the problem, particularly when geared at a similar motor speed / headstock speed ratio to that of the Myford when parting off.
 
As has been pointed out in the other thread on this, it's either deflections in the tool/workpiece interface and/or chip crowding in the groove being cut.
My view is that chip crowding is the main culprit as it's quite unusual to get a lock-up in the early stages of the cut, while the groove is still shallow.
 
Martin.
Thread: Rear mounting parting-off tools
12/01/2011 10:46:42
Provided that the workpiece itself is mounted rigidly, there can only be two causes for a cram-up.
Either the tool digs in somehow, due to something like backlash or bending of the support system, or there is chip crowding of the groove being machined.
 
In any particular situation, it might be worth experimenting to find which is the cause of this bother, by cutting a groove just a few thou' in from the end of a bar, such that the full width of the tool is utilised, but (apart from the thickness of this flimsy shim) one side remains open for swarf clearance.
 
If a cram-up still happens, then it must be that the tool is moving into the workpiece for some reason. If the problem disappears, it must be chip crowding.
 
Martin.
Thread: Rulers - my pet peeve
08/01/2011 11:58:56
Posted by Dave Jones 1 on 08/01/2011 11:36:49:
...I had the luxury of missing out of capital punishment in school! ...
 
Dave
 
 
 
 
Good job you did, or we wouldn't have the pleasure of your company
 
 
Martin.
Thread: New Year's Resolutions
01/01/2011 18:47:22
David.
I've submitted a couple of articles within the last six months, but I don't have any idea if they were suitable for publication.
How long should we leave it before either chasing it up, or giving up any hope of becoming published, as I'm forever mindful of how busy you must be? 
Also, do you tend to get in touch with the author before sending it to press?
 
Martin.
Thread: Which slideway oil is best?
31/12/2010 13:18:06
I can see no real downside to using any typical low viscosity modern day engine oil. It's designed for use in hot and cold extremes, where condensation exists and under other very arduous working conditions.

The talk of its unsuitabiliy is a little overstated in my opinion and seems to be based on the theoretical problems of it containing detergents which will hold particles in suspension - but why is that a problem and why would it be better for the swarf to remain in contact with the ways? It could be seen as academic anyway, given the likely film thickness.

By the same token, if you've got that much swarf floating around the headstock, then surely you'd be better off cleaning it out before filling with oil. I also doubt that much dirt will stay 'on the bottom' - detergent oil or not, with all the rotating components in there. After all, my wifes juicer/blender doesn't leave much down there once it's running at full pelt.
 
Martin.
Thread: Compression Ratio required
15/12/2010 17:29:04
Compression ratio is Swept volume + Unswept volume divided by Unswept volume. So a cylinder of swept capacity of 100cc plus combution chamber space of 15cc will have a compression ratio of about 7.66:1 which is low by modern standards, but might be a reasonable figure for you to start from.
If you still don't have good compression once the theoretical is right, then it's time to check the basics such as valves and clearances and the fit of piston and rings etc.
 
Martin.
Thread: lathe belt
07/12/2010 16:30:15
Posted by Dinosaur Engineer on 07/12/2010 16:00:42:
Maybe the toothed belt is used due to a small pulley being used  ( high torque at small radius) and the pulley wheel centres are close so that it's difficult to provide enough "wrap around" for a 'V' belt. A friction belt would be better than a "geared" belt as it's more likely to slip rather than cause mechanical damage. The equivalent ' v ' belt drive would probably need more space and/or a tensioning roller to increase the small pulley "wrap around" 
 
 
 I agree with all of that and would say that if a small 'toothed belt' drive pulley is used, then that is probably a bad thing in this instance, as the belt will be prone to shedding its teeth.
Poly-V belts are much better under these circumstances, due to their slim construction and will wrap around smaller pulleys than other V-belts, but do need to be properly tensioned.
If the lathe in question has inadequate tensioning arrangements then that might be why the maker went with a toothed belt design, as it is more forgiving if left loose.
Almost all other manufacturers use V-belts of one style or another.
 
Martin.
06/12/2010 16:56:04
Looks like it could be a good candidate for a Poly-V belt conversion, if you can get the right length.
 
Martin.
05/12/2010 12:16:18
Gordon.
Would it be a big job to change the pulleys and belt for something more current?
 
Martin.
Thread: Myford Squareness.
04/12/2010 23:11:41
Myford have a fixture - much like a long angle plate, which uses the relevent vertical shears to reference it at an accurate 90 degrees to the lathe bed, ie. nominaly parallel to cross slide movement. The saddle is then scraped on it's lower vertical guiding surface, so that a dial gauge when affixed to the cross slide, shows a very small positive reading when moved from the front towards the rear of the lathe. So in effect, the whole saddle/cross slide assembly is turned very slightly anti-clockwise when viewed from above, with everything within that assembly being machined at (nominally) 90 degrees and no special allowance is machined into the tee slots or other faces as this in built 'error' is so small.
 
Martin.
Thread: Endmill, Slot Drill
01/12/2010 12:58:44
The whole parting-off on a Myford thing has always intrigued me too.
My thoughts are that the problem is largely down to chip crowding in the groove as well as a slightly flimsy compound assembly.
So using coolant can help flush the chips, but as the chip is at least as wide as the slot, (but probably wider due to plastic flow) it can still get jammed and cause a cram-up. Turning the tool upside down and mounting at the rear allows gravity to help remove the swarf, but I find that the modern insert style tooling can be used conventionaly in the front position with confidence as the tips are designed to shrink the width of the swarf and thus enable easy ejection.
 
Martin.
Thread: levelling
29/11/2010 23:25:08
Terry.
There is no fundamental reason to have a lathe bed level in the sense that one would ensure a shelf or kitchen worktop is level.
The engineers precision level is used across the bed as a means of comparing readings between the headstock and tailstock ends of the machine until the difference either disappears, or becomes so small as to become negligible.
At that point, the bed is without significant twist, and can be relied upon to be accurate in use.
However, other benefits may become apparent from having a machine bed level, such as the correct drainage of coolant and being able to setup surfaces of castings etc with a level, secure in the knowledge it will be parallel the the machine bed.
 
Martin.
Thread: Chinese lathes
27/11/2010 18:39:06
Quote
"... Lifes too short for this kind of carry on....especially considering that John S, Tony, I and some others do not really need to be fighting WARCOs battles...
 
...Come to think of it, we now even have a belated confirmation from the original contributor that it wasnt really about a battle in the first place!..."
End of Quote
 
Then, there was a blinding flash - a puff of smoke...
...and the lights came on!!
 
Oooh-eer! I've gone all light headed! - This is how Pam Ewing must have felt when she woke from the worlds longest nightmare, to find Bobby safe and well and taking a shower.
 
Martin.
27/11/2010 12:04:46
Would somebody be so kind as to point me towards the text of impending legal action, by the owner of this lathe, as I seem to have missed all the fun?
 
Martin.
Thread: PRECISION , ACCURACY and QUALITY
27/11/2010 11:45:56
Do you feel the question has been asked with sufficient PRECISION to allow me to provide an answer of acceptable ACCURACY that would be of a suitable QUALITY?

Edited By blowlamp on 27/11/2010 11:47:47

Thread: Which New Lathe; choices, choices...
26/11/2010 21:04:30
Jason and Terry.
Thanks for the information on the Warco lathe.
Terry... I'm still sat next to Lathejack, peering at a soggy M300 lathe brochure, whilst crying my eyes out and thinking about what could have been with the £38.50 I have in my pocket.
 
Martin.
Thread: Chinese lathes
25/11/2010 00:25:19
Lathejack's reply in this post http://www.model-engineer.co.uk/forums/postings.asp?th=45283 hints at how long he has owned his lathe.
 
I must say that I see his Album pictures as being valid and valuable to the members of this forum as they show the reality of his particular situation.
He hasn't embarked on a rampage of insults against anyone and has only shown what he has found to be at fault with his equipment, as received from the manufacturer/vendor.
 
Martin.
Thread: Which New Lathe; choices, choices...
24/11/2010 23:08:59
Terry.
No, I don't think this lathe comes with Power Cross Feed, nor any change to the Tumbler Reverse mechanism.
While I'm here though, can you tell me what kind of chuck fitting your new Warco lathe has?
 
Martin.
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