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11

Show"N"Tell ( Your Machines) / DIY Epoxy Frame based CNC MILL

« on: January 21, 2019, 08:20:46 AM »

Hi all

Its been a while since I popped in here, been pretty busy work wise.... and not enough workshop time.



Anyway I have started building a new CNC Mill and have started a blog here: https://www.model-engineer.co.uk/forums/postings.asp?th=139042

As you can see the build uses Mineral Castings (Epoxy granite in the US) The molds and many of the parts are laser cut steel.

I decided to make it as small as possible due to my small workshop space is at a premium. As you can see it will fit into a 1 Metre (about 40") cube plus the stand. It will not be a light machine and will weigh several hundred kilograms a kilogram is equal to 2.2 pounds approx. the travels are 520 x 300 mm If I had more room I would have made the 300 mm 700 mm Z axis is 250mm clear under the gantry plus tool shank allowance. For the odd time I want more clearance I will use the manual V mill. Less Z travel should improve the stiffness.

I have a mach 3 license so will control it with that. Drives will be DC servos old from stock but in good condition.

Currently the cross-member and two columns are cast. the base is next maybe this week. Nearly all the components and the molds are laser cut steel already done. So far I am really pleased with the accuracy of the castings.

Anyway if you are  interested keep an eye on the thread I will keep posting as the build progresses.

Regards
John

12

General Mach Discussion / Re: Mach 3 Sewing Machine

« on: August 09, 2017, 09:03:55 AM »

And I am still around

A conventional "plain" sewing machine controls the stitch length by the movement of the "Feed dog" that pulls the material from underneath in short strokes. Best you study an actual machine to see how it works the length of stroke can be adjusted by a knob or lever in the sewing head. A few "walking foot' or "needle feed" machines also feed from the top but that is another story.

A typical plain sewing machine operates at around 5000 rpm (equaling 5000 stitches per minute),  however quilting is thicker than say shirt fabric and it is normal to reduce the speed to between 3500 and 4500 RPM. You reach a point where thread breakages become an issue, there is too much friction and the needle can become so hot it will melt the thread.    

However a frame quilting machine head mechanically or CNC driven does not have mechanical feed dog. To control the stitch length you need to match the feeding speed to the stitching speed using a ratio that that gives the right stitch length.

These days most quilting machine designs use a moving head in an XY frame, the fabric in its frame stays still, mechanically considerably more complex, the benefit being a greatly reduced machine footprint.

The machine will be heavy with a large moving mass even for a small design, This means that unlike a manually driven machine where the material is stationary when the needle penetrates the fabric the machine will be moving and so will the needle, this can be alleviated a little by a the foot on the machine that holds the fabric down the "Presser foot" but there will be some movement. in spite of the movement the system will work as long as the stitch to feed ratio is not too big. Typically the stitch length at 3500RPM can be around 3mm. Longer stitches will require slowing the machine down.

For any given material, thread and machine there will be a sweet spot, Its not unlike metal cutting in that respect.

On The Mach 3 side the objective will be to maintain a constant feed / stitching speed ratio. at any feed rate, if this is not done the stitch length will vary.

I cannot imagine Mach could handle moves on a stitch by stitch basis except at slow stitching speeds? However it would be a good feature for things like "Back tacking" at the start and end of a line of sewing. Some sewing heads can also trim the threads off at the start and end of a line of stitching that would have a subroutine (It has to back up the line it just did)

Lastly sewing machines are not perfect there are too many variables thread will break. A means of reversing the program back to where the break was and a little past it will be required.

It's been a while since I thought on this I wonder if Mach4 is better equipped to handle CNC sewing?

Regards
john McNamara

13

General Mach Discussion / Re: quilting or embroidery machine

« on: November 08, 2015, 12:59:28 AM »

Hi All

I am working on a quilting machine design. I just set up a breadboard system using MACH3 Smooth Stepper and a Homann designs MB02 Break out board. Running on a fresh 7 windows install to a clean hard disk.

I am using Brushed DC servos and Leadshine DCS 810 drives. Brushed is still a fair bit less expensive than AC brushless.

Its all up and running on the desk beside me.

To make a test pattern I used AutoCAD to draw a simple Diamond design, having done thousands of them in the past a few minutes work. There are only 2 polylines used The central pattern and the border. In the past I used a post processor Written in VB to generate machine code for a proprietary Italian Resta Machine (Not Gcode). This post processor was set up to "follow" polylines, only stopping at the beginning and end. In AutoCAD a polyline can have many segments compared to a line in AutoCAD that is a single object. (Polylines can include arcs).

Using polylines gives good control of the machine, For this test only two; and the starts and ends are all near zero. The pattern design does close the start and ends touch however they are not joined.

So what to use as a post processor? I tried the Lazycam beta program available when you install Mach, It worked!
But don't get excited yet, While it flawlessly converted the DXF file from AutoCAD (Saved as version 12) and ran on the test bed strange things happened.... The zero point was moved to the right hand side of the of the design and it started there, and it did not start at the beginning of the polylines it reordered the segments.

I am not familiar with LazyCam, there may be settings to correct the above inconsistencies. If anyone is more familiar with it can offer a suggestion I would appreciate it.

However settings or not it does the job and would machine the correct pattern. There will just be more jumps than needed. Note the pattern is 3365 mm wide by 3810 mm High. Jumps matter!

The final test will be to understand How accurate the constant velocity setting is in Mach ? from what I have read this is the best currently available option?

There is mention of the requirement in the Mach Laser setting?

As has been discussed a lot in this forum (Run a search on Quilting) It is very important the stitch length is maintained at all times irrespective of the feed.
 
In a perfect world one of the spare axis could be set to this mode.

Thinking on it there are many applications where some sort of work head speed has to be accurately correlated with the feed vector.

Applying Paint, Glue or other materials
Laser or flame cutting.
Sewing
Sign writing
There must be more

Regards
John

I tried to upload he image below to the page as an IMG but it did not work

Hyperlink worked...
http://www.mediafire.com/view/nil9a4j1ao22319/Quilt.jpg
http://www.mediafire.com/download/9vs61pvj21i8f3c/quilt_test_A.dxf

14

General Mach Discussion / Re: Constant velocity

« on: August 07, 2014, 11:16:05 AM »

PS:  This discussion on the Mach forum is worth reviewing.

http://www.machsupport.com/forum/index.php/topic,15212.0.html

15

General Mach Discussion / Re: Constant velocity

« on: August 07, 2014, 10:51:13 AM »

Hi NJ Lowie
Hi Hood

It may help to think of a quilter as a tube of toothpaste squeezing out material. You have to match the flow of the material to the feed over the surface you are applying it to.

A conventional sewing machine has a feed mechanism that is mechanically linked to the stitching mechanism. slow the stitching down and the feed will slow down in perfect unison.

Quilters are big. Very big. A large industrial one will have a moving mass of hundreds of kilograms. I had one that had a moving mass of about 500 kg. When it slowed down to turn a corner or reverse direction the stitching head had to slow down too. The stitching speed and the feed were not mechanically linked; the X-Y feed was CNC driven by a proprietary control system that maintained the relationship.

Quilters usually have not very stiff RHS Steel frames and a heavy sewing head, they flex. Fast reversal is not an option or they will shake due to vibration in the system. They have to be slowed down and then accelerated slowly.

A typical Sewing machine working as a quilter has a top speed of about 4000 RPM the length of one stitch is about 2.5mm (1 Stitch per Rev) That gives a top feed rate of 2.5 x 4000 = about 10 metres per min or 32 feet per min imperial down to about one stitch per second 60 rpm for "tacking" (At the start and end of a run to tie off the ends of the cotton to stop it unravelling).

The ratio must be kept constant to avoid the space between stitching holes changing.

A stitch length of 2.5mm is nominal depending on the work it can be as low as 1.5 and as great as 10mm for heavy mattress work or stitching polishing mops and other industrial products quilters are not just used for bedding. Many Car seats faces are CNC quilted. As are train and Plane seats, also Clothing, Parkas and dressing gowns etc.

I have never seen a satisfactory solution for this application using Mach3. Considering the (Thousands) of industrial quilters in the world and an order of magnitude more quilters that work from home. It would be a good problem to solve.

Regards
John

16

General Mach Discussion / Re: quilting or embroidery machine

« on: May 23, 2013, 07:30:13 AM »

Hi Eclipze

I Am not familiar with Art and stitch.

I have read that Dasault Draftsight (A free program) gives the ability to draw over an existing bitmap placed in the background on screen, as does AutoCad. I use this feature in AutoCad to draw over complex decorative shapes in Architecture. Just remember to scale the bitmap to the correct overall size before drawing the stitch path over it.

A long time back I used Corel draw to "vectorise" images.... Hmm it never worked very well, it created hundreds of short lines, and cleaning them up took forever. no good for a stitching program that ideally has a continuous line.

As mentioned scaling is very important, Your sister will have to know the finished size of the article before starting a design. The finished size is not the stitched size, She will find that once removed from the frame the article will shrink, between 4 and 10% depending on the thickness of the materials and the wadding. Once she has made a few this will become obvious.

You may like to mention to her that any design that has high density (lines close together) stitching in one place and widely spaced lines in another will will create a dimpled appearance due to the shrinkage mentioned above varying from one area to another. 

I fear your sister is in for a learning curve to learn the steps to get from design to machine, If this is to be a business it will be worth the effort.

Art and stitch at nearly a thousand bucks (950) is not cheap, Using a free cad program and DXF to G code converter for mach would remove that cost, and in the end she will have better control.

The is no need to learn the an entire CAD program, just learn the steps to get the job done...... starting at zero (0,0) lines, arcs, setting and scaling a bitmap,exporting to dxf layers and saving for a start, although once you start it is a great tool if you make things, she may get bitten by the bug.

Maybe I have missed it in the thread but I would be interested to hear how the machine is set up?

Cheers
John


 
 

17

General Mach Discussion / Re: quilting or embroidery machine

« on: May 23, 2013, 02:32:32 AM »

Hi Eclipze

We just used Autocad DXF file output to design Patterns for our Resta commercial machine. There are lots of programs that output DXF.

Our method was first to draw the pattern using any line type on a layer.

Then create a new layer and drawing on that layer trace over the previously drawn sketch using one or more continuous poly line and arc paths (using arcs and lines only). You only need to create a new path if you need to jump over the pattern without stitching some patterns never stopped at all no jumps is ideal if you can design it so.

Once the design was finished we deleted the sketch layer, exported the DXF file and converted it to Resta code A non standard G code. We developed that inhouse using VB.

There are a number of DXF to G code converters, Hopefully they will be fine with Mach.

Cheers
John McNamara





 

18

Show"N"Tell ( Your Machines) / Re: 4 axis bedmill retrofit

« on: February 14, 2013, 10:04:00 PM »

Hi Machine head

Thank you very much....

Cheers
John McNamara

19

*****VIDEOS***** / Re: Laser Cut Frame CNC Router New build

« on: February 14, 2013, 06:15:45 AM »

Hi Tweakie

The machine lives nearly 4 hours from me I live in Melbourne. It was done by us as a labour of love for the Men's shed (They paid for the materials).

The timing belt, in this case T5, worked quite well, Care was used in setting it up to the recommended tension. Note the long axis belt sits on an aluminium support so there is no flap. the idlers are ball bearings and as stated previously all rotating elements run in ball bearings. I think this is why the results were so good. I precision bored, after clocking them in the 4 jaw, all the timing pulleys to fit their shafts so there was very little off centre run out error. By reducing the error of the various parts to a minimum the total error was greatly reduced. The synchronising shaft was also carefully turned true on each end.

Note also the way the motor is isolated and the 3:1 reduction is fully supported and tensioned (The motor assembly slides).
The next one is going to use a similar belt driven design. For this one I would like to source zero clearance pulleys all round "Breco" make them and AT5 belting instead of T5. If the cost is reasonable. Alternatively I wonder if there is a good US source for zero clearance timing pulleys?

John

20

Show"N"Tell ( Your Machines) / Re: 4 axis bedmill retrofit

« on: February 14, 2013, 05:51:01 AM »

Thanks Tweakie

Gee there are a lot of utils there I will look for the Gcode tool......Mr sanders is in OZ too.... I live in Melbourne

John