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Messages - John Mac

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51
Tangent Corner / Re: Designer resource Sites
« on: December 14, 2008, 07:57:15 AM »
Hi All

A handy on line conversion tool.

Newtons pounds force ETC

http://www.onlineconversion.com/force.htm

A better explanation
http://www.seattlescience.com/2005/11/07/converting-pounds-to-newtons


Even Biblical measures Here
http://www.convert-me.com/en/

Cheers

John Mac

52
Tangent Corner / Re: Designer resource Sites
« on: December 13, 2008, 09:38:23 AM »
Hi All

Some usefull calculators.

http://www.handymath.com/calculators.html

Cheers

John Mac

53
General Mach Discussion / Re: Bridge Beam
« on: December 12, 2008, 07:07:44 AM »
Hi Tweakie

Around 60kg for the work head in this case is a sewing machine running at 4500 RPM (Always slightly out of balance and with a needle striking the work intermittently) causing load pulses.
There is a matching beam underneath as per my previous post re Mach 3 sewing.

I have worked on other machines of this type the vibration can be really noticeable; the last one from an Italian company used a similar sized box section.

Ideally a deflection of less than a thousandths of an inch is needed for good stitch formation. You can tweak that a bit. Come to think of it that should be your job!

I like the “I” beam as a concept the flanges form a natural cover for the slide ways and drive components. Using a box beam these would have to be shrouded with extra metal
The back of the “I” beam will be a perfect place to locate the flexible plastic duct for the power and air supply. 

The 310 beam has a mass of 32kg per metre the 250 x 150 x5 RHS used on my previous post was only a little lighter at 29.9kg per metre

A kg = 2.20462262 Pounds

It may be possible to downsize the beam. At this time I don’t know. Empirically most similar machines use beams between 250 and 300mm. so I chose the larger.

Cheers

John Mac

54
General Mach Discussion / Re: Bridge Beam
« on: December 11, 2008, 06:18:23 AM »
Hi All

Another way of reinventing the wheel.

This time I have used a length of 12 mm plate Laser cut with “H” pattern holes. Pairs of precision cut mounting blocks are inserted in the holes and backed up by a 5mm thick washer that covers the “H” holes. An M8 threaded rod and nut fitted between the pairs tightens the rail against the blocks.

The question for me is what sort of accuracy could be achieved by this system?
The plate would have to be mounted on a strong backing frame and carefully packed level. That covers one alignment plane.

The holes would have to be cut in one setting of the laser cutter as would the sides need to be trimmed to get parallel edges.

The blocks are a worry… They would need to be a decent fit in the holes.

One thought would be to put a hole in the washer and pump epoxy into the joints after manual fine tuning of the alignment is done.

The blocks themselves would reflect the error of the laser; Would the reflected error be consistent over a batch, it may pay to put a mark on each one with the laser (Say cut a corner off slightly) to enable them to all be oriented the same way when being installed.

I considered tapering the sides of the block at the insertion point, that possibly could make them lock in place but the tolerances would be hard to set up. Maybe putting a cut a few mm in from each side would allow a little give?

There is no drilling or tapping for this design. And it would be quick to set up., against that you have the cost of the Laser Jobbers time? And slightly higher material cost and weight.

Cheers

John Mac

55
General Mach Discussion / Bridge Beam
« on: December 11, 2008, 03:00:39 AM »
Hi All

Attached is a couple of images of a possible approach to a guide way.

I have used adjuster bars 20mm square Mild steel plus the pyramids to seat and precision locate the 25mm round shafting (Pre drilled at 120mm spacing as per the Thomson spec sheet)

These bars could be made on a small mill.

Ideally after rough cutting at the local plasma or laser cutter’s shop.
Only the ends, back and V’s would need to be machined. The rest could be left as is.
In fact there if the shop had one of the latest machines only a few thou would be left to finish square.

The spacing between the V’s could be set by milling one first then locking the table and using the first one as a reference for the other, for the final cut. If done carefully it should be possible to get it to a few tenths.

There is a fair amount of drilling and tapping to do, and a lot of alignment to set it up but the result should be “Spot on”. All the adjustments are lock nutted. The top and bottom adjustment jams the bar between the ends of the beam. The in and out adjustment is lock nutted through the web of the beam. Using the same threaded rod that is holding the Roundway.
Note the nut behind the bar to tension that. The holes in the web of the beam are drilled oversize to allow adjustement.
 
This beam 310 UB40.4 has a 6.1mm web. I guess that is the weakest link in this setup. It is beyond my ability to calculate the deflection under a load perpendicular to that face. But for wood or Aluminium cutting it should be fine? The illustration is about 1500mm long Although I plan to make it 3600mm long

It would be interesting to know the Deflection If any member would like to do it I would appreciate hearing from them. 

Just doing a bit of brainstorming at the moment, there may be a better way, in fact an alternative method is bugging me right now!

If it looks OK I will post it.

Cheers

John Mac

56
Tangent Corner / Designer resource Sites
« on: December 10, 2008, 08:10:46 AM »
Hi All

I stumbled on this site while looking for Cap screw dimensions... It Googled straight up.
http://www.roymech.co.uk/Useful_Tables/Screws/cap_screws.htm

Or Screws in general
http://www.roymech.co.uk/Useful_Tables/Screws/

Or Useful_Tables
http://www.roymech.co.uk/Useful_Tables/

Or The Home page
http://www.roymech.co.uk/

If you stumble on a link it is often rewarding to strip away the levels one at a time....You never know what you may find.

Cheers

Macka

57
General Mach Discussion / Re: Mach 3 Sewing Machine
« on: November 27, 2008, 06:37:52 PM »
Hi Dennis
Thank you for your thoughts.

The reason is floor space… These machines are big. you can save say 4x5metres = 20 square metres…. about 220 square feet by not moving the work.

The application I am working on is not quilting although the machine would be quite capable of doing it.

I did a lot of browsing with a search tool called Alibaba
http://www.alibaba.com/
Quite good for industry specific searches of the net
Attached here is a couple of machines that do not move the work:

Both made you know where.
Cheers
John Mac

58
General Mach Discussion / Re: Wire Alignment
« on: November 27, 2008, 02:46:12 AM »
Hi Rich

For testing: I first leveled the bed in the X and Y direction, then mounted the wire using some blocks milled from mild steel at each end of the bed. They were adjustable to enable the wire to be positioned exactly.
By moving the wire (not the jig) that aligned the wire to the bed, end to end. The wire was set low, level with the centre of the V’s horizontally, making all 3 in line, to avoid parallax errors.

The head axis is aligned to the bed by the front and rear V ways which showed the original manufacturers scraping marks, it is not adjustable I do not have an Autocollimator so used a precision 18” inspection grade square and a dial indicator swung on a bar mounted in the chuck, the alignment to the bed was fine. Horizontally it appears fine using a test bar.

The saddle prepared to be set in Moglice http://www.google.com.au/search?hl=en&q=Moglice&meta= by fitting inverted V blocks  with cap screws to the 4 corners of the saddle. They were adjusted jacking up the saddle until it was perfectly aligned in all planes using the level and careful measurement to set the lead screw and control bars back on axis. Then all that remains is to very carefully remove the saddle and apply the Moglice to the saddle V’s and replace it over the bed. The next day the saddle was removed and the squashed out epoxy trimmed away. Am trying to find the CD to post some photos.

Cheers

John Mac

59
General Mach Discussion / Re: Wire Alignment
« on: November 26, 2008, 07:44:53 PM »
A couple of images of the precision level and the measuring stage cludged up from scrap.

Cheers

John Mac

60
General Mach Discussion / Re: Mach 3 Sewing Machine
« on: November 26, 2008, 06:36:04 PM »
Hi Rich

I don’t think I can avoid welding and then getting the rail mounting points machined.
Attached is the solid model I am working with. It has not been optimized yet. Just a sketch to get the feel of the issues involved.

It shows ground shafting as the rail system.
I recently found a better deal with a Taiwanese rail so will use that instead.
It is a bit over a third the cost of a Bosch “Star” rail. 

http://www.hiwin.com.tw/Products.aspx?type=gw&subtype=gw_e2

Type 25 is a (Most of the time) reference to the size class of linear rail. When you check the specs most manufacturers have a system that uses the same mounting holes and overall height. The load capacity varies as does the quality and accuracy. You can not mix and match rails and runner blocks between manufacturers.
Cheers

John

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