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Robot Arm

jcdammeyer

John
Premium Member
Installed the boring bar. Tweaked it to just shave the hole round. Now it's about 25.14mm instead of 25mm but good enough to locate the motor and it still lines up with the screws. Time to order all the metric socket and flat head screws. And one more flange to make.

The photo also shows more clearly how the 14 ipm feed with the 1/8" mill was way to fast when conventional milling.
1690907211220.png
 

jcdammeyer

John
Premium Member
This one is better. Not the best yet. But better. At least the slots aren't all jaggy. I've ordered a bunch of flat head metric screws from Aliexpress. I still have lots of other parts to make before screws become an issue.

SecondTryBetter.jpg
 

jcdammeyer

John
Premium Member
This one is better. Not the best yet. But better. At least the slots aren't all jaggy. I've ordered a bunch of flat head metric screws from Aliexpress. I still have lots of other parts to make before screws become an issue.

View attachment 37115
Two small 'oops!' on these.
One: Is that the slots need to be located 1mm lower so there's more body for tension adjusting screws.
Two: I thought I was using a 90 degree counter sink bit. Turns out I don't have any at all. They are all 82 degrees and metric flat head screws have a 90 degree bevel.

So the question is:

Any suggestions for one over the other? One flute, 3, 4 or 6? Coated? Uncoated? The diameter of the large part of the countersink in the drawing is 0.37" so I'm guessing for the 4mm screws a 3/8" countersink is the ideal size.

There are also 4mm and 6mm flat head screws in this project with the largest bevel being about 12.6mm for the 6mm flat head screws.

I know that you can't use a large countersink on a small hole since the cutting edge at the point might be too large for the hole that is being counter sunk.

Oh and there are also these which look interesting.
 

LenVW

Process Machinery Designer
Premium Member
So after practising with the mill and CNC to make a stepper motor encoder holder back plate I thought it was time to get back to the robot arm.
Used the band saw to rough out two pieces of surplus material. Then square off and size the blanks to fit the drawing dimensions.
 

LenVW

Process Machinery Designer
Premium Member
Where did you source the stepper motors from ?
There seem to be a lot of Chinese DC motors in the web, but, the ‘quality‘ is suspect.

Have you come across any reliable brands for drives and motors ?
 

jcdammeyer

John
Premium Member
Where did you source the stepper motors from ?
There seem to be a lot of Chinese DC motors in the web, but, the ‘quality‘ is suspect.

Have you come across any reliable brands for drives and motors ?
Yes. I agree. A few years ago I bought one of these on Amazon. Hated it. High frequency noise when it was idle that drove me nuts. Sold it for half price to a friend who didn't care. It's still on his shelf the last I saw.
1690991062885.png

For the robot kit, unfortunately because there are so many planetary drives attached to different size motors that require holes in the back for encoders I bought this kit from StepperOnline but this time direct from China and not Amazon.
1690991339307.png

I also bought the drives from them. They were each cheaper than the two stepper motor driver chips I use in my ELS for the Z axis microstepper which is why I no longer supply the ELS with the drivers.

So having said that, when I had problems with the noisy StepperOnline I ordered, along with some AC Servo motors two stepper motor drivers from Bergerda. More expensive by about 25% but the difference in quality inside and the size of the heatsink for the same rating I think made it worthwhile. And no noise at all. Internally nicer quality.

I have not yet wired up or powered up these new StepperOnline motors and drivers. If they are noisy and whine I'll dispose of them and do something different. But the motors and planetary gear boxes were cheaper sourced as a kit.

StepperOnline now have an AR4 kit that has the encoders directly mounted to the back integral with the motors. Not sure about those either. And a new motor with integrated encoder that has a planetary gearbox with even less backlash. Apparently that was a problem.

The tiny motor driver is rated max 24V, the rest can go higher so one of these days I'll dig out a 24V supply and try them and report back.
 

LenVW

Process Machinery Designer
Premium Member
Yes. I agree. A few years ago I bought one of these on Amazon. Hated it. High frequency noise when it was idle that drove me nuts. Sold it for half price to a friend who didn't care. It's still on his shelf the last I saw.
View attachment 37138

For the robot kit, unfortunately because there are so many planetary drives attached to different size motors that require holes in the back for encoders I bought this kit from StepperOnline but this time direct from China and not Amazon.
View attachment 37139

I also bought the drives from them. They were each cheaper than the two stepper motor driver chips I use in my ELS for the Z axis microstepper which is why I no longer supply the ELS with the drivers.

So having said that, when I had problems with the noisy StepperOnline I ordered, along with some AC Servo motors two stepper motor drivers from Bergerda. More expensive by about 25% but the difference in quality inside and the size of the heatsink for the same rating I think made it worthwhile. And no noise at all. Internally nicer quality.

I have not yet wired up or powered up these new StepperOnline motors and drivers. If they are noisy and whine I'll dispose of them and do something different. But the motors and planetary gear boxes were cheaper sourced as a kit.

StepperOnline now have an AR4 kit that has the encoders directly mounted to the back integral with the motors. Not sure about those either. And a new motor with integrated encoder that has a planetary gearbox with even less backlash. Apparently that was a problem.

The tiny motor driver is rated max 24V, the rest can go higher so one of these days I'll dig out a 24V supply and try them and report back.
I would have thought that an integrated encoder would be more reliable.
Were the components that affected by the signal noise ?
 

jcdammeyer

John
Premium Member
I would have thought that an integrated encoder would be more reliable.
Were the components that affected by the signal noise ?
The motors for the AR3 version all use the same CUI encoder external to the motor. The stepper motors and planetary gears are mostly very small so if this project doesn't work out I dispose of the smaller motors and use the encoders on larger ones like Treadmill or other types. OTOH, the AR4 series with integrated encoders are more expensive because they include the encoder (but cheaper than using the CUI) but they are useless unless the buyer also needs encoder closed loop feedback on the motor.

That's my reasoning. I doubt more reliable.
 

jcdammeyer

John
Premium Member
So a few more parts have shipped. There's lots more but when they arrive I will have all the screws, nuts and washers for the robot arm.
1691888208477.png
I fell down a rabbit hole trying to do some LinuxCNC porting for the Raspberry Pi. My questions to one of the LinuxCNC forums on how to do something were reacted to in a way I haven't seen for quite some time. Apparently I'm a troll and not listening when I reply I don't understand what someone posted. So the Raspberry Pi and 1200x800 touch screen has been put back into the box and I'm back to working on the robot arm parts.

Still too hot to cast but I have enough raw material to at least make some of the metal bits. The one thing holding me up is the 90 degree countersink bit. I have a set coming from China but these from PA look interesting. The description says 90 degree point.


Does anyone have this set? I guess I can make a trip out but it would be a waste at the moment if they turned out to be 82 degrees.
 

LenVW

Process Machinery Designer
Premium Member
So a few more parts have shipped. There's lots more but when they arrive I will have all the screws, nuts and washers for the robot arm.
View attachment 37408
I fell down a rabbit hole trying to do some LinuxCNC porting for the Raspberry Pi. My questions to one of the LinuxCNC forums on how to do something were reacted to in a way I haven't seen for quite some time. Apparently I'm a troll and not listening when I reply I don't understand what someone posted. So the Raspberry Pi and 1200x800 touch screen has been put back into the box and I'm back to working on the robot arm parts.

Still too hot to cast but I have enough raw material to at least make some of the metal bits. The one thing holding me up is the 90 degree countersink bit. I have a set coming from China but these from PA look interesting. The description says 90 degree point.


Does anyone have this set? I guess I can make a trip out but it would be a waste at the moment if they turned out to be 82 degrees.

John,
It seem to be ‘buyer beware’.
Off shore manufacturers supply a variety of CSK fasteners.
(I pulled this comment from an American Machining forum.)



Flat Head Screws – What angles are standard?

Q: I have a customer who is looking for some Inconel flat head screws and specifically called out 100°. Is this the standard?

A: Flat head screws, also known as countersunk screws, are able to be manufactured with 6 different angles – 60°, 82°, 90°, 100°, 110° and 120°.
 

jcdammeyer

John
Premium Member
John,
It seem to be ‘buyer beware’.
Off shore manufacturers supply a variety of CSK fasteners.
(I pulled this comment from an American Machining forum.)




Flat Head Screws – What angles are standard?

Q: I have a customer who is looking for some Inconel flat head screws and specifically called out 100°. Is this the standard?

A: Flat head screws, also known as countersunk screws, are able to be manufactured with 6 different angles – 60°, 82°, 90°, 100°, 110° and 120°.
Good point. I have all the flat head screws. I'll take my protractor to them and measure. Should be interesting.
 

jcdammeyer

John
Premium Member
Step:
1. Drill 4mm hole
2. Countersink with tool measured at 82 degrees.
3. Add bluing to the hole
4. Insert 4mm flat head screw and spin with 2.5mm Allen wrench.
Notice the very thin line contact near the head of the screw.
1691959620562.png

5. Grab 8-32 flat head screw, insert and spin around.
This time the screw bevel removed a considerable amount of bluing. More than is apparent in the photo as the reflective shiny aluminum reflects the blue from the unmarked area. But a visual inspection shows a smooth removal of bluing.

1691959812731.png

Until the 90 degree counter sinks arrive I can't verify but I'd guess that the 4mm metric screw does have a 90 degree bevel as per metric specifications.
 

jcdammeyer

John
Premium Member
Well that was disappointing.
ON sale at KMS I though I'd give the 1/2" one a try. Each of the 5 cutting edges had a lip of metal folded over so they were anything but sharp. A bit of work with a flat diamond plate at least got rid of that lip and it's got a bit more of an edge now.

But, unlike the picture on the web page, the cutting edge is not straight. It's approximately 90 degrees but it's more of a curve than a straight line so one tiny point might be 90 degrees. Since it was packed with plastic formed over the cutter that wasn't apparent when I paid for it. Not until I got it home did I see how rough the sharpening job was. I'd guess a 20 grit stone...
 

whydontu

I Tried, It Broke
Premium Member
Of all the zillions of countersinks I’ve tried, overall the best results have been with these:


And the trick is low and slow. I use them by hand in a carpenters brace for aluminum sheet, and at the slowest speed on my drill press for heavier stuff.
 

jcdammeyer

John
Premium Member
I have a set like that in 82 degrees. But not 90. I have a set coming from China some time in early September.
 

jcdammeyer

John
Premium Member
Browsing around on the Aliexpress web site looking at harmonic drives for stepper motors I ran into this link. Not cheap if you want to buy it assembled and read to go. Doesn't look like it even has encoders on each axis.
1692827783459.png
 

jcdammeyer

John
Premium Member
Meanwhile I've 3D printed one of the parts to get a better handle on how to machine it. Since it has a tapered roller bearing on one end and 8mm shaft on the other for a toothed belt pulley I don't think cast material will be strong enough. And I happen to have some 2.188" diameter aluminum stock.

J6-3D_printed.jpg

I'm thinking that cut a piece to slightly longer and face off and centre drill each end along with the hole for the 6mm screw. Then between centres bring the 17mm end down for a clearance fit for the bearing and to the correct length along with the shoulder for the inner bearing race.
Then flip end for end and turn the 8mm shaft for the pulley and the shoulder.
Next transfer to the mill and use the 17mm 5C collet and 5C spin indexer to hold the large end and support under the 8mm shaft.
Except I don't have a 17mm collet and 11/16" is too big. Really wish I'd finished my Harmonic Drive and the chuck and all that so I could mount the ER32 collets which are metric.

Hmmm. I could use the small rotary indexer to mount the ER32 collet chuck.

ER32HoldingJ6Body.jpg
Connect my ELS with internal stepper motor driver to it be able to spin it 90 degrees to square each side along with cutting the groove and boring the hole.
Like this:

I'm now glad I 3D printed the model of the J6 housing. More tangible as to what I need to do.
 

LenVW

Process Machinery Designer
Premium Member
For 40 years, I have been designing industrial equipment and using 82 degree FHCS.
Food Processing - Kelloggs
Plastics Extrusion - Big O Machinery
Millwrighting Projects - Central Ontario Metal
Vacuum Applications - SIHI Engineered Systems

This week was the first time I ran into 90 degree FHCS’s.
Apparently, Asian manufacturers have not conformed to the 82 degree CSK ???
 

jcdammeyer

John
Premium Member
From what I've read the metric version is 90 degrees while the imperial is 82 degrees.
BTW, the replacement DIMAR 202-C-12 5 flute countersink arrived via purolator today. It does measure 90 degrees and the quality is considerably better than the one picked off the shelf in a vacuum wrapped package. Came in a small plastic box. Very sharp. Much better looking. Even the hex shank.
So hats off to DIMAR for support!
 

whydontu

I Tried, It Broke
Premium Member
From what I've read the metric version is 90 degrees while the imperial is 82 degrees.
BTW, the replacement DIMAR 202-C-12 5 flute countersink arrived via purolator today. It does measure 90 degrees and the quality is considerably better than the one picked off the shelf in a vacuum wrapped package. Came in a small plastic box. Very sharp. Much better looking. Even the hex shank.
So hats off to DIMAR for support!

From 40+ years of selling industrial equipment. The difference between a poor supplier and a good supplier isn’t price, quality of the goods, or delivery. The differentiating factor is what happens when something goes wrong. Good suppliers fix the error without arguing.
 
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