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Jolt & friends - Team Overkill - NSW
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miles&Jules
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Location: ipswich QLD


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Whats the grunt of the new lathe like compared to the little old one?
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Post Sat Feb 04, 2017 10:53 pm 
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Nick
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On paper the new lathe is only 50% more powerful but in actual use, its more than that. I haven't had it slow down even slightly yet. The biggest difference is the stiffness; there is hardly any tool deflection when cutting aluminium and some of that could be due to me still using 12mm tool holders from the old mill.

The only bad news is that the better quality DRO from the old lathe is not compatible with the scales on the new lathe and I am stuck with the cheapo DRO unless I buy new scales - probably not worth the effort.
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Post Sun Feb 05, 2017 8:11 am 
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miles&Jules
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Not worth the effort - somthing i thought i would never hear you say Nick ha ha😎
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Post Sun Feb 05, 2017 10:00 am 
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Nick
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Laser testing:

The laser is cutting MDF but I found a few minor problems:



The test file uses layers to run up to 20 speed & power settings at once; in this case its 20% power and 5mm/sec up to 23mm/sec. The problems found so far: top cover switch doesn't close unless I lean on the cover, the origin is set at a random point near the centre of the table and the table probably isn't level.
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Post Sun Feb 05, 2017 8:21 pm 
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Glen
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Looks about right, the 40w lasers do 3mm MDF on ~450-600mm/min

Have you tried a test cut at an angle to determine a good focal length yet? That helps quite a bit.
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Post Sun Feb 05, 2017 8:57 pm 
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Nick
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I didn't think of the focus test, thanks for the idea! I got a little plastic spacer (which I almost threw away!) that is supposed to help set the focus. It must be close but in the test cut, the left side is focussed better - the 10 mm cut popped out while the 8 & 9mm barely cut through.

The next test is to set the origin to the top left corner, focus it there and then do cuts in each corner to see if the table is level. Once that is sorted, I can do that ramp test and be confident the table isn't contributing to the tilt.
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Post Sun Feb 05, 2017 9:24 pm 
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Nick
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Laser tuning:

The table isn't level but definitely not as bad as I feared;only 3.1mm between the highest and lowest spots:



There are some hard to reach locking nuts to undo and then the acme nuts can be adjusted to level the table out. After that, Glen's focus test can run to double check the factory focus spacer, which is likely wrong.

After that, the laser needs a power curve calibration with a calorimeter (fancy meat thermometer) and an ammeter.



The laser power output VS input current is not at all linear and there is a steep curve at lower power that levels off after 50% power and is virtually flat after 70%. Increasing over 70% power is supposedly just shortening the tube life for no extra power output so its important to know howfar to push the tube without damaging it.
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Post Mon Feb 06, 2017 7:47 pm 
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Nick
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Possible new flame thrower:

This burner for a camping stove has real possibilities:







The secret sauce in this stove is that it uses liquid propane from the inverted gas tank to get a higher flow rate. The liquid gas vaporises in the brass tube wrapped around the burner before its mixed with air in the long brass tube under the burner.

The flame from the flat burner is already quite long; in a dark room the flame is around 100 to 120mm. The original burner can easily be cut off and replaced with an open tube burner for a longer flame and the electrode for the piezo igniter can be re-used with an electric igniter that can be R/C controlled.

The air mixing tube under the burner gave me an idea; a sliding brass collar can be slipped over the tube and actuated with a servo so that it covers the air inlets to produce a large orange pure butane flame of uncovers the inlets for a hotter blue flame.

There is one downside to this liquid burner; it takes a good 10 seconds for the flame to go out after the gas is turned off at the tank. The gas control solenoid will have to be very close to the burner and maybe after the gas vaporising tube.
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Post Sat Feb 11, 2017 3:01 pm 
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Nick
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more flame thrower:

Here is a photo of the disassembled burner:



The thread where the hose screws on to the brass tube isn't a tapered gas thread and I can probably figure out what it is and get a die to cut a new thread. This camp stove is such a good performer that I don't really want to cut it up for a robot, so I will try re-creating the important parts from scratch like this:


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Post Sat Feb 11, 2017 5:15 pm 
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chunkulator



Joined: 27 Jul 2016
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Several blowtorches that I pulled apart use this arrangement too. A critical part of the design will be ensuring that the vapor tube runs close to the flame because the heat it what makes it vaporise fast enough to burn (which is why it wraps around the burner on your stove).

I considered this for Flamin Heck but couldn't find a way to do it safely given that the hot part is mostly outside the robot and the vapor tube is before the valve. If the vapor tube protrudes outside the robot where the flame is and somebody punctures it you will have liquid propane pouring onto the floor of the arena. My conclusion was to do this safely you would need two solenoid valves - one before the vapor tube. Or you need to come up with a clever way to keep the vapor tube in the hot zone but still protected.

Post Sun Feb 12, 2017 8:01 am 
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Nick
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I noticed the vapour tube has a braided steel rope inside it:



Its probably to distribute the heat more evenly and provide more surface area, are there any other ideas about it's function?

I had a couple of ideas about protecting the tube. The burner produces a large flame almost immediately, so it can't take much heat to vaporise the gas. While there must be a minimum length for the main burner tube, there probably isn't a maximum length, so the tube can be long enough to wrap as many turns of vapour tube as needed and still keep everything safely inside the bot:



The vapour tube can be brazed to the main burner tube for better heat transfer and the back of the burner tube has a large brass or aluminium slug to retain heat. Heating the burner assembly before the match with a pocket gas torch should help the gas vaporise before the burner heats itself up.
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Post Sun Feb 12, 2017 12:32 pm 
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chunkulator



Joined: 27 Jul 2016
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Seems like it could work, as long as you have enough heat at the back of the tube. The other idea I was thinking about today was to use an electric heater inside the bot. Maybe bits from a 3d printer hotend or something like that. Then you got put it anywhere you want.

Post Sun Feb 12, 2017 7:47 pm 
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Nick
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Location: Sydney, NSW


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That could definitely work; hot-end heaters are compact and convenient and it would be easy to make a small aluminium block to transfer heat into the vapour tube - excellent idea!

Laser power:

I did some laser output VS power percentage setting tests and put them into a graph:



It is not linear (as expected) and there is a huge kink around 30%, so extra testing either side of that is needed. The maximum tube output is 83 watts at 65 % power, which is is a little low but about what other users report for a generic Chinese tube.

The next step is to collect up samples of material to cut and run more speed VS power tests to get ideal settings for each one. MDF, plywood, HDPE and EVA foam are top of the list.
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Post Sun Feb 12, 2017 8:06 pm 
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Nick
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Back to actual bot building:

Its about time to get busy on Sportsman bots; the easiest one to finish is Mr T the flipper. I laser cut a new test chassis in 3mm MDF:



I can already see a couple of over-sized screw holes but the MDF model will be good enough to test fit all the internal parts and make improvements before cutting a new MDF prototype. MDF is cheap and now that cutting it is so quick, its possible to do several prototypes a day.

The cutting showed up another issue - the mirrors in the laser are wildly out of alignment and it took triple the usual power to cut the MDF so tomorrow's job is to do a full mirror alignment and clean. There may also be a problem with low quality mirrors and lens, which can be checked with the power meter. If there is a serious power loss from dodgy optics, its possible to buy higher quality replacements for not much money.
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Post Tue Feb 14, 2017 8:11 pm 
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chunkulator



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What will Mr T be made of once the MDF version is perfected?

Post Tue Feb 14, 2017 8:24 pm 
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