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  #1  
Old Tue 14 August 2007, 14:33
Hovernut
Just call me: Hovernut
 
Orlando
United States of America
Longer Z Axis or 5 Axis

Hi,
I'm glad to have found this forum via CNCZone. The MechMate looks to be the most promising of the DIY machines.

I'm a hovercraft manufacturer and am looking to automate my mold-making processes. Problem is, contracting out to have someone carve out a full-size plug to make my mold off of is going to cost several tens of thousands of US $$$'s, so, I'm looking to build a machine to do this myself.

I was curious if the MechMate is scalable in the Z axis so I can churn out a plug for a full-sized hovercraft: 22' long x 8.5' wide, and 4 or 5' in height for either plug.

I'd be carving 20 pound density foam, and maybe tooling putty, so the side loads shouldn't be all that much, therefore affording a longer Z axis than what would be allowed for wood or metals.

Also, would it be possible to fabricate a 5-axis head....adding a B and C axis to the spindle to get compound curves on the formed surface?

We use Rhino for design, and would likely use RhinoCAM or MadCam do drive the machine.

Any help/advice in this quest would be greatly appreciated!!

Cheers,
John
Orlando, FL
www.hovernut.com
www.amphibiousmarine.com (tooling for the 'Explorer' model)

Last edited by Hovernut; Tue 14 August 2007 at 14:35..
  #2  
Old Tue 14 August 2007, 16:23
Bill McGuire
Just call me: Bill
 
Weiser, Idaho
United States of America
Hovercraft

Cool...

So after your hovercraft projects, will you be building a MechMate that'll handle some smaller jets? If so, you might just want to build it a little larger to begin with...

Saw your site... nice machines...
  #3  
Old Tue 14 August 2007, 16:43
Hovernut
Just call me: Hovernut
 
Orlando
United States of America
Quote:
Originally Posted by Bill McGuire View Post
Cool...

So after your hovercraft projects, will you be building a MechMate that'll handle some smaller jets? If so, you might just want to build it a little larger to begin with...

Saw your site... nice machines...
Funny you should say that! Just a couple weeks ago, my friend, the hovercraft company owner, and I visited/toured Composites Unlimited in Oregon. They have a large 5-axis machine they use for aerospace and other applications. They do, in fact, manufacture a sleek 2 seat jet from the tooling that thing made; http://compun.com/clients.html Oh, by the way, they ballparked a figure of about $250 per square foot for the finished plug!

Like I said, I don't need aerospace tolerances, just a mm or tenth of an inch will do just fine!

Now, if I could just get a hold of the plans for this, http://www.rainnea.com/cnc_5axis.htm I could scale it up to do just what I need!!

Cheers,
John

Last edited by Hovernut; Tue 14 August 2007 at 16:51..
  #4  
Old Tue 14 August 2007, 22:50
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Hi John

As interesting as it sounds, I personally cannot offer you much help. But it would be interesting if other guys used this thread to explore some ideas . . .

The motor power, gearing, racks and electrical controls of the MechMate would all be okay for what you want to achieve. Things I would look at to achieve your abjective:

- Double the distance between the two tubes/rails of the gantry.

- Double the wheelbase of the y-car.

Doing the above will increase the "footprint" area of the Y-car 4 times. This can be done with minimal thickening of plates/material. The x and y rails will have to be longer to accommodate the extra wheelbases.

- Redesign the z-axis. Counterbalance the z-axis with a pneumatic cylinder or a weight hanging over a cable pulley.
  #5  
Old Wed 15 August 2007, 00:40
Hovernut
Just call me: Hovernut
 
Orlando
United States of America
Gerald, thanks for the general guidelines. Still pouring over the net, I found a fella in NZ who makes a B+C axis attachment that turns a 3-axis into a 5-axis: http://www.doughtydrive.com/products.html

Anybody have a MechMate running or under construction in Florida or the Southeast for a looky-loo? Being an airline pilot, I can fly almost anywhere to get a look at a machine.

Thanks,
John
www.hovernut.com
  #6  
Old Fri 17 August 2007, 01:21
Daya
Just call me: Fabrica
 
Kandy
Sri Lanka
Hovernut, What is the price they are quoting or the 5 axis attachment.
  #7  
Old Fri 17 August 2007, 01:22
Daya
Just call me: Fabrica
 
Kandy
Sri Lanka
Hovernut, What is the price they are quoting or the 5 axis attachment and also what is the software your planning to use to work with the attachment.
  #8  
Old Fri 19 October 2007, 07:43
Steven Ree
Just call me: steve.r
 
British Columbia
Canada
John
If you go to
http://www.talkshopbot.com/forum/mes...tml?1191000042
this saved us thousands and do this in house! Use cout3d by vectric and cheep foam board coated with epoxy.
Steve
  #9  
Old Sun 04 November 2007, 05:52
joepardy
Just call me: Joe
 
Lebanon, OH
United States of America
Gerald,

As mentioned in other posts, I am in the process of designing a B-C head - and make the MechMate unit a 5-axis machine. I have pretty much finalized the design, and it looks like the head will be about 8"x8"x8" and will weigh around 75 pounds.

I am looking to build a machine that has a 24" Z-axis, so it is quite possible that the total weight of the moving portion of the Z-axis will weigh around 150#.

While looking through other posts on this website, I have see suggestions of using Linear Bearings from VXB. I have been looking at their 25mm twin block slide units. The block costs about $60. The block & a 60" shaft cost about $130.

My though was to design the Z-axis using 2 shafts and 4 blocks. Total cost including the pillow blocks would be around $450 + shipping.

The "slide" would be a flat plate 6" wide x 40" tall with a 3"x3" steel tube attached to the back. The portion attached to the gantry would be virtually identical.

Questions:
Do you think that a 3x3 steel tube will be stiff enough to keep the Z-axis from "bending" when extended out?

Do you think that there would be much "chatter" generated using linear bearings?

What are the tradeoffs to using a Linear Bearing instead of the more traditional rollers? I planned on doubling up the blocks so that I would have about 10" of block sliding up the 25mm shafts.

Dust?

Any insight would be appreciated.
  #10  
Old Sun 04 November 2007, 06:14
garyc
Just call me: Garyc
 
Charlotte, North Carolina
United States of America
I use vxb bearings on my router for the x & y axis, They work ok for me. BUT I would not use them for your application, The reasons why are because mine do have some play in them, and they are not adjustable like others are, and they have no way to lubricate them. So when you install them what ever play you have is what you get, plus to lube mine I have to squirt oil on the shafts, then if I get a little to much it drips all over. I would think that you would get chatter and a lot of it especially when you extend the z distance. I am thinking of replacing mine because of the chatter I am getting. I have been using mine for about 1.5 years. To get by building a cheap, first time router they are good but anyone using them will soon find out the same things I have, and will probably replace them like I am going to. Thats why I have been dreaming of building a mechmate. My router can cut about 25" X 52" and I ended up spending about as much as a full sized mechmate would have cost me if I had known about it at that time.
  #11  
Old Sun 04 November 2007, 06:36
joepardy
Just call me: Joe
 
Lebanon, OH
United States of America
With regards to lubrication, these bearings have grease fitting installed in them.

I appreciate your comments regarding chatter.
  #12  
Old Sun 04 November 2007, 08:29
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Joe, are you talking of those bearing blocks that run on round shafts? If so, how would you attach those round shafts to the "flat plate 6" wide x 40" tall with a 3"x3" steel tube attached to the back"?
  #13  
Old Mon 05 November 2007, 02:42
soulvoid
Just call me: Håvard
 
Stavanger
Norway
Quote:
Originally Posted by Gerald D View Post
Joe, are you talking of those bearing blocks that run on round shafts? If so, how would you attach those round shafts to the "flat plate 6" wide x 40" tall with a 3"x3" steel tube attached to the back"?
I'm going in a similar route as someone gave me 4 linear bearings and two round shafts. I'm thinking of attaching the shafts to the plate, the shafts came with mounting blocks. I would think that this would allow the longest stroke and stiffen the plate up somewhat but there would be room a 2x2" steel tube too, 3x3" would be pushing it. The bearings would go on a plate that screws into a plate much like the spider plate. My z shafts would be more like 24" total(cannot quite remember the length now) so the stroke would far less than 24", more like 12". The shafts are heavy, but I don't think it matters much. Been thinking of using a aluminum plate for the z to try to keep the weight down, but the weight savings are so small and I doubt the motors will have any problems holding the z axis, especially with the weight compensation of the gas spring.
  #14  
Old Mon 05 November 2007, 03:47
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Those round shafts are actually quite flexible. If you only fix the ends of the shaft to a long plate, you must add the flex of the shaft to the flex of the plate - you get double flex. Not half.....double.
  #15  
Old Mon 05 November 2007, 05:59
joepardy
Just call me: Joe
 
Lebanon, OH
United States of America
Actually, yes, I was thinking of using the 36" long 25mm round rods (Kit7234) attached only at the ends. Advantage - grease fittings.

However, I could also use the 20mm rail guideway (Kit7429) reinforced with a plate and 3x3 or 4x4 steel tube. Advantage - attached at full length. Disadvantage - no grease fittings, "open" bearing

What I am looking for is a means to travel about 24" (Z) - yet remain very rigid (X & Y)
  #16  
Old Mon 05 November 2007, 06:56
driller
Just call me:
 
A comment, not a recommendation, but Kit 7429 is attached the full length, so it will provide more strength than just end mounts.

Keling has actual linear rails and blocks. full length and I think stronger.

But, when you put the motor out that far, you increase the leverage on the cart on the Vee bearings.

I would check with Gerald to see where the center of gravity (center of axis points?) would be.

It seems to me that such a long axis is getting away from the actual engineering of the machine itself.

The machine design is based on some solid engineering, and some things will not change anything. A longer X axis will have zero effect. A longer Y will require some increase in strength of the cross rails. I'm not sure what other thing(s) might be effected by a longer Z.

Dave
  #17  
Old Mon 05 November 2007, 07:03
joepardy
Just call me: Joe
 
Lebanon, OH
United States of America
Based on some other posts (I think in this thread), I was planning on changing the width of the gantry - which should help stabalize the Z Axis.

Bottom line - I figured that I would have to beef up X & Y to compensate for the BC head and the longer Z
  #18  
Old Mon 05 November 2007, 08:28
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Joe, I would want to see drawings of the head before I can offer anything more constructive. Volume/space in which the cutter moves, and in which the motor bodies move.
  #19  
Old Mon 05 November 2007, 09:25
Marc Shlaes
Just call me: Marc
 
Cleveland, OH
United States of America
Send a message via Skype™ to Marc Shlaes
I can't find anything where Joe said the purpose of the machine. Cutter loads are negligible if he is only cutting foam. Somewhere he probably said, but i didn't find it.
  #20  
Old Mon 05 November 2007, 09:52
joepardy
Just call me: Joe
 
Lebanon, OH
United States of America
Gerald,

Can you send me your private email address? I would rather not make my design public at this time.

With regards to what I am cutting - it will vary between MDF, Plywood, Foam, and Fiberglasss.
  #21  
Old Mon 05 November 2007, 10:55
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Sorry Joe, I am not going to get into an off-forum discussion on this one.
  #22  
Old Mon 05 November 2007, 11:15
joepardy
Just call me: Joe
 
Lebanon, OH
United States of America
No Problem.

In a nutshell, the head is an 8" cube. The router (Standard Porter Cable 7518) would mount to the side of the cube, the Z-axis would mount to the top.

I also drew up a lighter weight design. On that one, the head was a 6" cube - same router mounting - same z-axis mounting. But I thought that the gear interface wouldn't be adequate.

In both cases, the "cube" includes the motors, gearbox, bearings, mounting plates, etc.
  #23  
Old Mon 05 November 2007, 12:11
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
So the tip of the cutter could at times be about 10" away from the center line of the z-slide (router horizontal)?
  #24  
Old Mon 05 November 2007, 12:23
joepardy
Just call me: Joe
 
Lebanon, OH
United States of America
Probably not that much. Assuming that the slide will be reinforced with a 3x3 tube, the BC Cube would be mounted to the underside of that tube/slide unit. Both the B & C axises are located in the center of 8x8 cube - so if my geometry is correct, I am guessing that the center point of the router bit would be about 6" from the center point of the z axis.
  #25  
Old Mon 05 November 2007, 13:02
joepardy
Just call me: Joe
 
Lebanon, OH
United States of America
Gerald,

Not sure if I am posting this right, but I am attaching a conceptual drawing of the BC-axis and where it attaches to the Z axis.
Attached Files
File Type: pdf Mounted BC Axis.pdf (4.4 KB, 189 views)
  #26  
Old Mon 05 November 2007, 17:20
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Isn't the Porter Cable 7518, with 1/2" cutter, much fatter and longer than what you are showing?

The point I am going to make is that the cutting loads are applied way off the center line of the slide, which makes it bend and twist. Imagine the loads on your wrist if your walking stick had a serious Z-shape - and then try and push the walking stick sideways through sand . . . . . .

Going from 3-axis to 5-axis introduces a much higher level and range of forces. Plus you have all the additional pivot and gearing points for backlash. On the MechMate side you can increase the wheelbases to get firmer footings - particularly for the z-axis rollers. (the top z-rollers placed higher up and braced back to the edges of the y-car)

A 3"x3"x1/8" tube, added to the front of the "gauge" plate will help a lot. But you have to get a tight bond between the tubes and the plate to get it really strong and resist twisting. Consider welding up the slide, straightening and stress relieving it and then have it machined for V-edge straightness.

Try to widen gauge plate from 4 to 5 inches
  #27  
Old Mon 05 November 2007, 18:07
joepardy
Just call me: Joe
 
Lebanon, OH
United States of America
The drawing was just a conceptual drawing. I don't have dimensions of a PC7518.

Thanks for the advise on the slides.
  #28  
Old Mon 05 November 2007, 22:30
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
I was asked whether a 3"x3" tube will be stiff enough to support a concept? (A definite yes/no reply wanted to a definite dimension . . . . doing a vague job. Just not possible!)

Do yourself a favor, and draw your definites to scale - you already quoted the motors, gearboxes and router. Think you would be in for a surprise with your "cube" size.

That's enough of these time-waster threads!

Thread closed.
  #29  
Old Fri 24 October 2008, 17:55
Woodchuck
Just call me: Stew
 
Southeast Iowa
United States of America
Modifying to 5 axis?

Moved from elsewhere:

Hi everbody I am new to this forum and this is my first posting. This
question might be for Gerald D but maybe others could answer
My question is if this machine was built and learn to operate it could
this design be modified later to apply a B/C axis head to the Z axis
and lengthen the Z out to 16" , it would also mean making a tall tower for
the carriage and the table could stay the same? I would like a 5 axis machine
in the end or would it be better to build a seperate machine to have the 5 axis capability? You could machine things with out repositioning them or
building special fixtures. Thanks for your time
  #30  
Old Fri 24 October 2008, 23:04
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Better to build a separate machine
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