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[CNC] CNC from sketch to part the way I do it

Dan_S

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#91
I am using both a stepper and servos on my mill, all with a single loop via magnetic scales. All of the velocity feedback that is required comes from the magnetic scales, there is no need for an encoder on the motor unless the servo drive requires it. There is no under or over shoot, it goes where it is told to go and is accurate to within plus/minus 1 pulse. In my case, 1 pulse is 0.000039 inches (1 micron).
ho are you dealing with screw flex and twist, and all the other forms of backlash, with a single loop sevo system? Are you deriving the velocity and acceleration inputs from the position inputs of the scales?


it's good to see more programmers showing interested in hobby cnc and I hope they can get something to market in an affordable price range, I
I don't think it's a software issue, as much as it is the nature of the beast. with all the possible hardware combinations I think it would be cost prohibitive to design and build a control that handles everything really well in a plug and play fashion. The number one thing the industry does, is buy matched drive and motor sets. They are essentially plug and play, because someone did the toning for you, but they are super expensive and only work well as a matched set.
 

JimDawson

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#92
ho are you dealing with screw flex and twist, and all the other forms of backlash, with a single loop sevo system? Are you deriving the velocity and acceleration inputs from the position inputs of the scales?
Yes, the only position inputs the controller sees is the feedback from the scales. The update rate is so fast (about 62 uS) that the motion profile is very smooth. Of course, you have to properly tune the system for the mass and motors to get things to work correctly. This compensates all of the backlash and other errors, the controller calculates everything by position over time.

I can usually manually tune a system in about 5 minutes.
 

jumps4

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#93
In this video I try to show how I adjust my gigs without over-tightening them
I hope this makes sense, I keep saying 1.8 or 1. something as an amount of travel, I mean 1.8 of a thousandth
sometimes I have problems expressing to others what I'm thinking. the brains running I just cant get my mouth in the right gear.
thanks for viewing
steve

[video=youtube;S6RELpadoTQ]
 
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angelfj1

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Active Member
#94
In this video I'm going to start showing what I have learned about gibb adjustment and backlash compensation. i'll have to break it up into a few videos to keep them short, that away I'm already set up to do what I want to show.
I'm not trying to be a know it all and any corrections are more than welcome.
hobby cnc machines are different in the fact they have to deal with a lot more friction and adhesion problems not encountered in factory machines with roller linear rails, guide ways and massive ball screws . there are ways to improve these faults but not eliminate them totally in a hobby cnc conversion.
I chased my own tail for years until I understood what was happening under my mill table.
In this first video I talk about what I have learned about adhesion, torsion, friction, flex and stored motion
thanks for viewing
steve

[video=youtube;CfsiZ-6D0W4]http://www.youtube.com/watch?v=CfsiZ-6D0W4&feature=youtu.be[/video]
Steve: Not to worry about having a college degree or not. You have demonstrated that you are a true professor regarding the operation of these hobby mills.
Two words come to mind; brilliant and practical.

Keep it coming.

Frank
:))
 

angelfj1

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Active Member
#95
I did some research about a year ago on direct reading scales in each axis directly reading table movement and their use with mach3 and emc2 and at that time the only controller card I found that would support linear scales with custom written software was kflop by Dynomotion. I spoke to the man that designed the card and wrote the software for it and he said he could write me the software but the best mach3 could do with the information was to stop if a preset error level was triggered. if mach3 thought it was at one reading and the scales showed a different reading it would stop mach3 from running. at this time mach3 would not support error correction by moving the axis to where it should be or stop the travel if it is going to overshoot. I figured I could do that by measuring the part after the software ran and didn't invest in it until better software comes around at a hobby price. maybe mach4 will be able to self correct but it's still in beta. when they finally figure out how to do that the sloppiest machine built will make great parts because it wont allow an error to take place. that's going to require a lot of processor speed and programing to look ahead and determine prior to it taking place there will be a problem.
steve
Steve: I'm ordering a G0704 this week, before Grizzly's 10% sale is over. Before I order the components for a CNC conversion, I intend to give Dan (Hoss) a call and ask about his new , not released yet (PhaseIII) CNC conversion for the 704 type mills. From what I have read so far, he intends to use double ball nuts. Since I don't really know what this means, I was wondering if double ball nuts are used to address some of the problems you have been discussing in these latest posts, e.g. error levels, etc. What do you think?

Frank
:))
 

jumps4

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#96
hi frank
I have single ball-nuts in my machines and they all seem to have about .0015 thousands backlash. for my use and the fact mach3 compensates for this I could not see the expense of 2 ball-nuts (plus loss of axis travel to make room for them ) unless I was going to larger screws to eliminate as much torque in the screw as possible also. If I was to build another mill I'd put the screws outside the table instead of under so I could use a 25mm screw and then yes double ball-nuts. Just adding my 40lb vise to the table weight adds another .0015 of backlash due to the screw twisting.
I try to keep myself in the lower cost hobby use of cnc and chasing the last little bit of accuracy will have you pulling your hair out thinking about room temperature, material temperature, load on table, cutter force.
It's more knowing your machine than buying the best parts. I'm not making parts that require perfection in every area so if I really need a perfect circle in an exact spot I'll have the cnc cut it small and then I'll pull out the boring bar to finish it. I use my cnc to get the bulk of the work done and then I bring it into spec as required. It is easy to make certain sections of your part undersize by telling your cam software your cutter is a few thousands larger than it really is. this leaves material for you to remove later to come into spec. you can always take more off but putting it back on isn't that easy.
steve
 

angelfj1

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Active Member
#97
hi frank
I have single ball-nuts in my machines and they all seem to have about .0015 thousands backlash. for my use and the fact mach3 compensates for this I could not see the expense of 2 ball-nuts (plus loss of axis travel to make room for them ) unless I was going to larger screws to eliminate as much torque in the screw as possible also. If I was to build another mill I'd put the screws outside the table instead of under so I could use a 25mm screw and then yes double ball-nuts. Just adding my 40lb vise to the table weight adds another .0015 of backlash due to the screw twisting.
I try to keep myself in the lower cost hobby use of cnc and chasing the last little bit of accuracy will have you pulling your hair out thinking about room temperature, material temperature, load on table, cutter force.
It's more knowing your machine than buying the best parts. I'm not making parts that require perfection in every area so if I really need a perfect circle in an exact spot I'll have the cnc cut it small and then I'll pull out the boring bar to finish it. I use my cnc to get the bulk of the work done and then I bring it into spec as required. It is easy to make certain sections of your part undersize by telling your cam software your cutterSteve is a few thousands larger than it really is. this leaves material for you to remove later to come into spec. you can always take more off but putting it back on isn't that easy.
steve
Thanks Steve. As usual you make perfect sense. Can you say a little more about why a double ball nut is used?

Frank
 

jumps4

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#98
sorry Frank
after reading my reply again I see I never answered your question. :nuts:
my single ball-nuts have .0015 backlash because of clearance between the balls and the housing and screw. the ball-nuts with circuit tubes you can remove. you purchase larger balls to remove this backlash. double ball-nuts have a spring in between the 2 nuts forcing them away from each other to take up this backlash. double circuit ball nuts are different also because they have two circuits of balls and are built for heavier loads.
steve

double nut graphic.jpg bouble ball nut.jpg double circuit ball-nut.jpg double circuit ball-nut graphic.jpg
 
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jumps4

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#99
while on the subject of backlash I want to mention these BK style preload bearings for the end of the ballscrew from china. All the parts are there to make a really good bearing but they come out of the factory defective ( I have installed probably 20 of them ) the inner and outer races of the opposing bearings are the same height so without a spacer installed inside between the two outer races you cannot add preload to the bearing by tightening the nut on the ballscrew. this only makes the two inner races contact each other before pressure is being applied to the outer races. a thin spacer installed inside the housing between the two outer races fixes this problem and removes all the backlash from the bearing.
steve

bk style preload bearings.jpg
 

angelfj1

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Active Member
while on the subject of backlash I want to mention these BK style preload bearings for the end of the ballscrew from china. All the parts are there to make a really good bearing but they come out of the factory defective ( I have installed probably 20 of them ) the inner and outer races of the opposing bearings are the same height so without a spacer installed inside between the two outer races you cannot add preload to the bearing by tightening the nut on the ballscrew. this only makes the two inner races contact each other before pressure is being applied to the outer races. a thin spacer installed inside the housing between the two outer races fixes this problem and removes all the backlash from the bearing.
steve
Steve, this is very interesting but its a lot of trouble and $$$ for a hobby machine. You have already shown how Mach3 can compensate for backlash!!!

Frank
 

jumps4

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It has been a while since I have done any drawing in here so I took the time to record making a part for an old steam engine project I haven't worked on in about 4 years. I'd like to get this thing done and out of my shop but I burn out working on it from time to time. I probably first began this project 8 years ago.
this first video shows what the part will be and how I designed it.
thanks for viewing
steve

[video=youtube_share;2lJefp80Vwo]

- - - Updated - - -

this video shows some cad corrections in Emachineshop and converting the drawings into g-code in D2NC
thanks for viewing
steve

[video=youtube_share;Ipazd_GoXEY]
 
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jumps4

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this video shows machining the profile on one side of the part, I didn't record everything
there are also pics of the part as the machining progressed;
.
thanks for viewing
steve

[video=youtube_share;RZP6IOqbgzI]

DSCF1213.JPG DSCF1212.JPG DSCF1211.JPG DSCF1210.JPG DSCF1209.JPG DSCF1208.JPG DSCF1207.JPG DSCF1206.JPG DSCF1204.JPG DSCF1203.JPG DSCF1202.JPG DSCF1201.JPG DSCF1200.JPG DSCF1199.JPG DSCF1198.JPG DSCF1197.JPG DSCF1196.JPG DSCF1195.JPG DSCF1194.JPG DSCF1193.JPG DSCF1191.JPG DSCF1190.JPG
 
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jumps4

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this is a photograph of the finished shaft coupling installed. I may rough it up a little to look like a cast part.
steve

DSCF1214.JPG
 

jumps4

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I haven't given up here I'm just trying to get my model done and out of my shop. it has been 6 years off and on. I would put it aside until my skills got better then start working on it again. I'm finally ready to finish it. Since I plan On giving it to the town where the mill is located I'm hoping to get locals there to donate a Glass enclosure and cabinet.
http://www.hobby-machinist.com/showthread.php?t=6463&p=206763#post206763
steve
 

jumps4

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Something happened today I thought I would share with the group, in my e-mail I received a nice compliment and invitation From Emachineshop.com. They are asking others and myself who have made videos about Emachineshop on YouTube to assist them with short videos In their monthly Newsletter. I guess my videos weren't as boring as I thought.
That is really nice of them to ask me and I'll post my reply after I have spoken to them about what is involved.
Steve

" To:jumps42009
Hi,
We were happy to see your videos on YouTube featuring the eMachineShop free CAD software.
We are developing a section in our monthly newsletter showcasing those that have made YouTube videos using our software.
Would you be interested in becoming a showcased designer/machinist in our new section?
We are aiming for short videos that move quickly through instruction. So if you are interested, please reply back with a few recommendations for review. As an fyi, we will link directly to your YouTube channel.
Looking forward to your reply.
The Best,
Dawn
eMachineShop.com "
 

kgaby

Swarf
Registered Member
Steve, I have learned alot from your videos. Thank you for taking the time to share your knowledge. I am very new to cnc and you have been a great help to me in learning. Thank you!
 

Rick Leslie

Active User
Active Member
Something happened today I thought I would share with the group, in my e-mail I received a nice compliment and invitation From Emachineshop.com. They are asking others and myself who have made videos about Emachineshop on YouTube to assist them with short videos In their monthly Newsletter. I guess my videos weren't as boring as I thought.
That is really nice of them to ask me and I'll post my reply after I have spoken to them about what is involved.
Steve

" To:jumps42009
Hi,
We were happy to see your videos on YouTube featuring the eMachineShop free CAD software.
We are developing a section in our monthly newsletter showcasing those that have made YouTube videos using our software.
Would you be interested in becoming a showcased designer/machinist in our new section?
We are aiming for short videos that move quickly through instruction. So if you are interested, please reply back with a few recommendations for review. As an fyi, we will link directly to your YouTube channel.
Looking forward to your reply.
The Best,
Dawn
eMachineShop.com "
It's awesome that the software company wants you to do a short tutorial on their product! I need to go to the Youtube channel and check out the videos. I know you explained the modeling process better than I found anywhere else. This thread is what kept my interest in my little CNC conversion and helped the project progress. I was lost once I got ready to model until your thread.

Thank you from a CNC/CAD newbie!
 

jumps4

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It has been awhile since i have added anything to this thread and I finally have a project I think will be interesting and challenging to add.
I was recently contacted by Bill Gruby about assisting him making 2 parts for his 18 cylinder Radial engine build.
( ADD Bills thread here )
I was a bit puzzled by Bill's request because if any of you know Bill he is very interested in Cnc but honestly doesn't need it to accomplish
the many things he builds and shares here in the forum. I have yet to see anything he could not make and was sure he could make these parts.
Bill mailed me the prints for the 2 cams for the engine and the directions for machining them manually that were included with the plans.
The challenge became immediately apparent as I read the directions and imagined myself trying to follow them and what my end results would have been.

To just machine out the cam lobe profiles on on the rotary table there would be 280 separate 1 degree moves of the rotary axis and the Y axis that
have to be at the same time, meeting at the same end point to ensure a good finish. you would have to keeps in mind the machines backlash and reset the dial to zero for each change in y axis direction.
that is a .001 to .003 move in y and 1 degree of table movement 280 times to complete 8 cam lobes. and there are 2 of these cam rings.
If you tried to move one axis then the other the finish on the part would be a series of very small steps around the entire profile that would need to
be finished smooth by hand when done.
reading each line of the directions then preforming the move without any mistakes and not getting a headache would be beyond anything I have ever done.
one mistake and the part is scrap and there are 2 of these that need to be exact to run right.
anyone who knows 4 stroke engines and the effect of any changes to a camshaft have on performance would see the problem here.
these cams can be made and the motor will run but the difference is in how smooth and steady the motor runs can very a lot.
this is a real determining factor in how all the work to everything else made comes out in the running of the model engine.
So with all that said how will I do this on a Cnc 4 axis mill is the next question and the answer was not as easy as I expected.
there are different types of 4th axis functions and most wont work for this part.
In most 4th axis setups on a Cnc mill the rotary axis is mounted standing up facing the z axis from one of the four opposing directions available
X+ X- Y+ and Y-.
Different types of cam software's do different types of operations from different locations of z to the axis. z axis centered behind or in front of the
center of the rotary axis is used to make things like gears.
for my examples the rotary axis is mounted on the left side of the x axis facing z.
for the setup I just described the x axis moves back and forth as the y axis increases the depth of cut and z doesn't move.
when each operation at that location completes y backs out from z the the rotary axis turns to the next location and repeats the operation.
this is 4th axis indexing and can be done with z above or to the side of the center of the rotary axis.
This operation will not work for a cam lobe.
the next type of 4th axis operation is called wrapping.
wrapping takes a drawing that is in x y plane and converts all the y or x moves ( determined by the rotary axis location )
into rotary axis rotation at a given circumference. if the y or x axis length 2" then you will wrap that around a circle with a circumference of 2".
z is lowered on each line and follows it at one set depth. raising and lowing to cut each line.
This will not work to cut a camshaft.
the next type of rotary axis operation is rotary axis turning. in this operation the rotary axis rotates and the cutter removes material at a set z depth,
like a lathe operation.
this won't work for a cam lobe.
the next operation is rotary axis contour turning
in this operation the rotary axis rotates and the z axis moves up and down and the x axis side to side as the part is rotated
this can make a cam lobe but only with a ball end mill and the finish would be a series of lines around the cam as the cutter moved in x direction.
this would be smoother than hand making the part and more accurate but would still have to be hand finished.
you can't cut the profile in one pass with a flat bottom end mill eliminating the ridges a ball cutter would leave because the flank side of the cutter
as z moved down would cut
into you lobe as it lowers.
If I did do it with the ball end mill and decided the finish would be acceptable to polish out, the end mill would have to be less than an 1/8" because the
cam lobes in each row are that close to each other.
this will not cut bills cam to the desired result.
so to do this with a standing rotary axis to a close to desired result the y axis will have to move also so the cutting surface on the flat cutter moves
from center to flank as the z axis lowers and face to center as the z axis raised and the cam lobe rotation crosses center. since the
face and flank shape of the cutter contacting the lobes will be concave and the lobe would have to be cut by stepping in from the side in small increments
to keep from leaving lines like the ball end mill.
this software for for this type of 4th axis operation is very expensive and I don't have it.
this is Not an available choice for bills camshaft from me.

Since 2006 I have tried demo software's whenever available and I have never seen the 4th axis operation I need for this project
I want to cut with the side of the cutter so the cutter will not leave lines around the circumference. one finish pass at a set depth from start to finish.
to do this the rotary axis has to be mounted on the mill table facing up centered with z axis and all the moves to make the lobes have to cut in
either y or x direction away from zero.
the reason I haven't seen this approach to rotary axis is because a Cnc milling machine can cut this shape without the need of a rotary axis. by moving x and y in any direction
it can cut any shape. makes sense right.
well not for Bills cams.
on Bills cams as your looking down on the print there are undercuts that come in from the sides with the part mounted in this direction.
the cutter has to step in from the side below the upper cam to cut the lower cam.
I'll have to cut this from the side with a Woodruff key seat cutter.
problem solved? well almost. true I can set the z height to the correct cam lobe height then with the software I have move in and cut the cams Outside diameter by moving the x and y axis until I have moved all the way around the part, lower z and repeat for the next cam shape.
then move out and up to clear the upper lobe.
a little hand coding and it could be done that way.
well not with my machine and mach3.
mach3 backlash compensation works perfect in a linear move but has trouble working in an arc. I have .0015 backlash in x and in y.
the end result will be four or more bumps in the surface of the cam where mach3 compensated for the backlash.
where to go from here...
I have it figured out and I know how to accomplish what I need to do but I'm tired of typing and will post how I'm going to do it and show what I am doing in another series of posts with pics and maybe videos .
Thank you for viewing
Steve
 
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jumps4

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here is a photo of a cam and the followers in a radial engine and two pics of the plans I have
the pics are blocking certain parts because they are copyrighted and are here for just an example.
these are plans and not cad files so in order to machine these parts in a cnc mill i have to draw them
exactly to spec and make the g-code from my drawings.
to start with I need a top down view of each cam with all 8 lobes, intake and exhaust. there is a front and a rear cam so that is 2 drawings like these.
they will be used to rough away the material from the top down in conventional cnc milling.
sometimes you can copy a print and trace it into a cad program to get what you need but this will not work from
these drawings because they are copies of copies and the lobes seem to be hand drawn.
so I have to draw from measurements.
the plans have location measurements for every degree of angle and the distance from center for that point including the radius of the Woodruff key seat cutter.
so I have everything I need to draw these cams.


DSCF1813.JPG DSCF1834.JPG Radial EngineCamshaft and Follower.jpg
 
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jumps4

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this engine has 9 cylinders per bank front then 9 rear, 18 total
there are four cam lobes for the front nine cylinders intake and 4 exhaust. that means that each time the crankshaft turns 2 rotations on number one cylinder, the cam is on the next set of lobes for number one cylinder. there are 4 sets of lobes so the engine rotates 8 times before it gets back to the original set of lobes for number 1 cylinder.
with 2 cams and 18 cylinders the engines fires 9 cylinders every revolution.
that part has nothing to do with cad or cnc but was just too kewl to not mention
Steve
 

jumps4

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I noticed in the directions to mill this part manually that the cam lobes have the same shape on their approach to cam follower as leaving the cam follower. this means that once I have drawn one half of one lobe the reverse side is a copy flipped over and rotated into position.
that will complete one lobe. I Then copy that completed lobe and rotate it 90 degrees and that the next lobe. i copy the last lobe made and rotate each 90 until all 4 lobes for the circle are done. I then connect each lobe with a line on a 1.5 radius and I have the complete intake cam drawn. the exhaust is done the same with its measurements.
I tried that first that is the machining path of the 1/2" cutter not the drawing of the part.
I could use this to cut the part out and it would be right but it is not a cad drawing of the part it is the path the tool needs to follow . For my needs
when I rough out the part I want to leave .005 clearance by telling D2nc that my .500 cutter is .510. this will leave .005 around the entire part for a finish pass.
so shorten the lines by .250 because the cutter is a half inch and and then connect the tops of all the lines right. that removes the cutter.
no, that will draw a lobe but it does not include the tangent of the cutters edge contacting the material as it turns it shows only the y axis point of contact.
in order to draw the correct shape of the lobe I had to draw all the lines extending out from 0 in 1 degree increments. place a .5 circle on top of each line and intersect the tangent of each circle to the one next to it. delete everything else and the tangents are the true cam lobe and the shape the cutter will leave.
I hope these pics are in the right order.
Steve

DSCF1814.JPG DSCF1815.JPG DSCF1816.JPG DSCF1817.JPG DSCF1818.JPG DSCF1820.JPG DSCF1821.JPG DSCF1822.JPG DSCF1823.JPG DSCF1824.JPG DSCF1825.JPG DSCF1829.JPG DSCF1830.JPG DSCF1831.JPG DSCF1832.JPG DSCF1833.JPG
 
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jumps4

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photo number seven shows 2 circles one red overlapping the first drawing.
the circles represent the cutter and if you notice in the red circle there is part of the first drawing. that is why i had to use the tangents to draw the lobe.
the material would not have been removed following the first drawing and did not represent the true cam lobe shape.
Steve
 

jumps4

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Once I had the cam profile drawn I made this video to show how I produced the outside contour roughing g-code
Thanks for viewing
Steve

 

RJSakowski

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Here is another video, this one goes into the d2nc cam software and then to mach3 with the drawings I have made in the previous video.
If anyone has anything to add, comment on, or critique please do. I'm not an instructor on any of these software's but that is probably why no one is doing this. they think they have to be. I make mistakes and find corrections... I hope this helps get someone else started.
If i'm learning by my mistakes I have to be a genius by now... lol
I get the impression from what I read that quite a few people think they need complete training on their cad, cam and operating software from a college or online course to do this and my point is for me it is easier to learn as I go.
A quote from Einstein I like is something like this " don't waste space in your brain memorizing anything you can look up "
If you have any ideas what to go into next, let me know, if there is none I guess I'm done for now.
thanks for watching
steve


[video=youtube;VXizFzP6rAw]

note: sitting in a quiet room and talking to yourself for an hour is a weird feeling, try making a video.
For someone who is not an instructor, you do a awesome job! I use SolidWorks now but have used a number of 2D drawing CAD packages in the past including Vellum, AutoSketch, various versions of AutoCAD, and Daftsight. eMachineshop looks as it would be far easier to learn. I will pass on the recommendation to anyone looking for a good CAD package and the recommendation to catch your YouTube videos. Thank you for sharing!
 

jumps4

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Thank you RJ
in this video I try to explain how the hand code is written to come in from the side and cut the cam profiles.
I st-udder and stumble as the squirrel in my head trips over my tongue but I make it through and I hope you can understand what I'm doing.
the video flickers this time, I just did the video before this one with no problem.
hopefully you can follow along, these are not easy to record without something going wrong.
Thanks for viewing
Steve


 

jumps4

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I'm on hold on the last project waiting for the materials so I have started a new project for a friend of a friend
These parts will be for the tail rotor of an RC helicopter.
I'll try to document everything from start to completion of the machined part itself.
I make a lot of mistakes and there are changes as I go along but I hope it is helpful for others.
These are not how to videos but more how I'd do it videos, and suggestions or alternative ideas are always welcome.
I'm looking for a way to make a video of actually machining the part in fast forward so i can show the entire machining process.
I had to use the same thumbnail for a couple videos because YouTube was messing with my upload, but they are different in content.
Steve






 

jumps4

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In video 36 at 2:45 in I set the depth of cut to .6 for the side view op , that is a mistake. the depth of cut should be around .385. I'll correct in the final g-code but I'm not going to make another video of it.
Steve