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  #1  
Old Tue 20 November 2007, 18:41
Art
Just call me: Art #2
 
Lancaster,Texas
United States of America
Extended Z-axis vibrates - stiffening spider plate

I am getting vibration with Z at full extension(12") and I think that it is caused by flex in the spider. I think that I have much more travel than Gerald designed for. I am thinking in replacing the spider with a 1" thick aluman plate 18" tall with 1" thick by 2" wide steel spacers for the 6 or 8 v rollers and a 1/2" thick z slide. Comment please.
  #2  
Old Tue 20 November 2007, 23:02
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
The spider-plate was supposed to be 4mm thick, but some ended up at 3mm thick. JR measured the flex in his "thin" spider and found it to be very little. The Mamba drawings make it clearer that 3/16" plate should be substituted if 4mm is not available (The first drawing now also states to expect flex if lengthening the z-slide).

However, I don't think that your spider is the major source of the flex - the "gauge plate" slide itself is the more likely culprit.

Would be interested to hear how those alu plates work out for you. Remember that the extra mass will need counterbalancing.

The longer z-axis drawings are for those who want to make foam molds and have light cutting forces. This is a territory I prefer not to venture into. Rember that the MechMate is "promoted" as a board processing machine because I know that is what it does really well.
  #3  
Old Wed 21 November 2007, 07:06
soulvoid
Just call me: Håvard
 
Stavanger
Norway
Quote:
Originally Posted by Art View Post
I am getting vibration with Z at full extension(12") and I think that it is caused by flex in the spider. I think that I have much more travel than Gerald designed for. I am thinking in replacing the spider with a 1" thick aluman plate 18" tall with 1" thick by 2" wide steel spacers for the 6 or 8 v rollers and a 1/2" thick z slide. Comment please.
Why does it vibrate? Does it happen when just moving without cutting? Does it happen when running the router without moving? How much does it vibrate? How much does it flex?

Sounds like you want to do whatever you can by uping the dimensions to stiffen it up. All that weight your adding with those dimensions might be enough to dampen the vibrations...
  #4  
Old Sat 09 February 2008, 13:31
Alan_c
Just call me: Alan (#11)
 
Cape Town (Western Cape)
South Africa
Send a message via Skype™ to Alan_c
Z Slide Assembled

I assembled the Z-slide today, had it machined at an engineering works I use for most of my maintenance work for the factory - not entirely happy with the end result, I get so frustrated when I know what I want and how to do it but dont have the tools at my disposal

I decided to go with the 6 wheel option on the spider even though I have a pre-Mamba unit, its close to the edge but works - as an aside I notice the spider has quite a bit of flex, if you lift the guage plate out of the bottom set so that it is only held by the top four rollers, the bottom pair spring back inwards slightly - when the plate is lowered again it seems to catch as it enters the rollers. Admittedly it was very roughly set up, will have to play with it some more once its fully assembled with spindle, gas strut and power.

Attachment 948

Attachment 949

As you can see I have added the cable chain mounting point as per the Mamba design - building a hybrid Classic/Mamba Mechmate

Started cutting the Y axis angle iron for the rail - the cutting jig works great but seems to use disks at a rapid rate, went through 3 1/2 disks to cut just one rail, and no I wasn't pushing too hard. When the disk is new, it cuts with a good flow of sparks, but once past halway, the sparks get less and the disk wears at a much higher rate. I was using the thin (1mm) disks from both Norton and Klingspor. The Norton ones wore down much faster.

As I didn't have any more disks on hand and the closest supplier is over the Mountain, I decided to call it a day and join the Kids in the pool (temps over 30 deg C today, but predicting thunderstorms for tomorrow)
Attached Images
File Type: jpg y car front.jpg (45.4 KB, 633 views)
File Type: jpg y car rear.jpg (45.9 KB, 634 views)
  #5  
Old Sat 09 February 2008, 14:13
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
The flex you see, ie. the v-rollers "bending" apart for the slide and springing back when the slide is out, is about right. I think it is also the 8mm bolts flexing a bit. All this doesn't seem to cause any problems though.

The good cutting disks are by Pferd - ask them for the thin Inox (Stainless Steel) disks.
  #6  
Old Sun 10 February 2008, 09:05
Art
Just call me: Art #2
 
Lancaster,Texas
United States of America
Z vibration solved

Here is my solution to prevent zibration and flex in the Z. Milling on the side of columns produces more laterial forces than the MM sees during normal router work. The back plate is .5" al and the side pieces are 1" by 2" solid steel. Produced a back plate that was HEAVY and requires a sledge hammer to get it to flex. Used 6 #3 V rollers like the Mamba. I probably cut the back plate off 1" above the top V roller in the future to reduce the weight.
Attached Images
File Type: jpg Z1.jpg (34.6 KB, 640 views)
File Type: jpg Z2.jpg (34.9 KB, 643 views)

Last edited by Art; Sun 10 February 2008 at 09:08..
  #7  
Old Mon 11 February 2008, 00:44
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Let’s analyze the loads on the bearing wheels:

Height from table to highest (upper) wheel: 400mm [16”] (approx)
Distance between upper & lower wheels: 170mm [7”] (approx)
Cutter load: 20kg [45 #]

Load on lowest wheel: 400/170*20 [16/7*45] = 47kg [103#]
Load on highest wheel 47-20 [103-45] = 27kg [58#]

Already it can be seen that the bottom roller carries nearly double the load of the top roller. If there is spider flex, one must look for it at the bottom roller.

If we recalculate for slide only 100mm [4”] longer the loads become:
Load on lowest wheel: 500/170*20 [20/7*45] = 59kg [129#]
Load on highest wheel 59-20 [129-45] = 39kg [84#]

Lengthening the slide only 100mm [4”] changes the loads by:
Upper bearing: 44% increase
Lower bearing: 26% increase
(I think that Art went more than 4" longer, but he did the clever thing to raise the upper rollers for that case.)
  #8  
Old Mon 11 February 2008, 00:51
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
So, what can we do?

I'll work on some sketches to stiffen the spider - it should be relatively simple. Must not interfere with dust hose. I think it could be done as an easy attachment to the current spider. Folk could decide for themselves if they want to stiffen it or not.

Something to look out for in the time being. . . . .
Check your bending of the spider to see if the eccentrics have a really flat surface to sit on. They might be rocking a bit?
  #9  
Old Mon 11 February 2008, 01:05
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa

Four (or only 2 at the bottom) flat bar stays can be inserted as follows:

  #10  
Old Mon 11 February 2008, 07:07
Alan_c
Just call me: Alan (#11)
 
Cape Town (Western Cape)
South Africa
Send a message via Skype™ to Alan_c
I was thinking along these lines: a brace welded across the back of the spider as indicated by the red lines, this will remove any flex in the plate - I hope?


ps in last paragraph of post 7, 10mm [4"] should read 100mm. Fixed - thanks
  #11  
Old Mon 11 February 2008, 08:18
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
I am not yet convinced that the spider plate is too flexible. Yes we can find ways to stiffen it, but we must first measure if we are going to fix something that is not broken. Somebody needs to rig a dial gauge as below:


Whatever stiffener is decided on (if proved necessary), must:
1. leave lots of space for a dust hose
2. miss the bracket for the z-motor
3. require minimal welding to reduce distortion.

I want to emphasise that folk must check that the wheels sit down flat against the spider - there is a bend very near to the roller position, and a slightly curved plate will allow the roller to rock.
  #12  
Old Tue 01 April 2008, 19:56
Robert M
Just call me: Robert
 
Lac-Brome, Qc
Canada
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Did any one measure some flex as per Gerald dial rig suggested ?
Just curious. Sorry if I can’t help or measure it, I’m only at the drawing & planning stage !
  #13  
Old Mon 07 April 2008, 08:38
Robert M
Just call me: Robert
 
Lac-Brome, Qc
Canada
Send a message via Yahoo to Robert M Send a message via Skype™ to Robert M
Gerald,
Would increasing the slide tube 10 40 360 and/or slide plate 10 40 330 thickness help in any way the flex ?
On the other hand, increasing either one or both, can this have some negative effect?
From my preliminary drawings, it appears having no interference effect ?!
Not wanting to suffer or to be jugged for the “bigger is better” syndrome, but would like to learn / explore more on this thought ?
Thanks, Robert
  #14  
Old Mon 07 April 2008, 09:47
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Quote:
Originally Posted by Robert M View Post
Would increasing the slide tube 10 40 360 and/or slide plate 10 40 330 thickness help in any way the flex ?
First show me what is flexing and then I will tell you how to fix it.

Art reported some flex, but his application is rather different. He also found that his motors could not hold his loads . . . . plus a few more things that we have never seen while cutting boards.
  #15  
Old Tue 08 April 2008, 17:26
ekdenton
Just call me: Ed #8
 
Alamogordo, NM
United States of America
Quote:
Originally Posted by Robert M View Post
Gerald,
Would increasing the slide tube 10 40 360 and/or slide plate 10 40 330 thickness help in any way the flex ?
On the other hand, increasing either one or both, can this have some negative effect?
From my preliminary drawings, it appears having no interference effect ?!
Not wanting to suffer or to be jugged for the “bigger is better” syndrome, but would like to learn / explore more on this thought ?
Thanks, Robert
Can I take a shot at answering your question Robert?
Robert, Increasing the thickness of the z-slide plate would not stregthen the design in the direction that I think you are saying. I can pick up a 10ft piece of 3/16 x 6 flat bar laying on it's side and the weight of the bar will cause it to flex. Then I can take a 1/4 or 3/8 inch bar the same length and it will do the same thing (maybe only a very slight difference). The weight of the bar will cause it to flex. The shorter the bar the less flex. The wider the bar the less flex in the width direction.

The tubing is 2 x 1 x 11ga., far as I know they don't make that size any thicker. 2 x 1-1/2 x 11ga tubing is a common size, but that may require a whole redesign of the spider to accomidate the extra 1/2 inch depth of the tubing.
hope that helps
Attached Images
File Type: gif untitled.GIF (7.1 KB, 397 views)
  #16  
Old Tue 08 April 2008, 19:36
ekdenton
Just call me: Ed #8
 
Alamogordo, NM
United States of America
Sorry I said 2 x 1-1/2 was a common size but I meant to say 3 x 1-1/2. I don't think 3 x 1-1/2 would fit without alot of redesigning.

I think what I will do if I have the flexing or vibrating problem I will just raise my workpiece closer to the gantry or use a smaller bit and slower feed rates.
  #17  
Old Tue 08 April 2008, 23:06
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Good drawing Ed!

IF flexing of the z-slide is a problem, and that is a big IF, then 10 40 360 S can be replaced with solid steel instead of tube. The (gas)spring will then have to carry a further 3.5kg [8#] . Alternatively, or in addition, 10 40 330 S can be increased to 8mm [5/16"] thick - that adds 0.8kg [1.8#].

But, I believe that you will be barking up the wrong tree. Art, who saw some vibrations in his application, cured his vibrations without modifying the z-slide. We can emulate his modification by adding simple stiffeners to the spider plate (10 40 430 W)

Please read post #11 in this thread again. At the end of that post is an important statement which I have now changed to bold text.

I believe that Art got his improvement for 3 reasons:

1. He used a stiffer spider (his first one was only 3mm [1/8"] thick (A 4mm plate more than twice as stiff as a 3mm plate)

2. His V-Rollers now seat down onto a flat surface.

3. He increased the distance between the top and bottom rollers:

  #18  
Old Tue 08 April 2008, 23:26
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
An experiment when you are bored. . . . .

Take two plastic rulers and feel how flexible they are. Feel in which direction they are flexible as well(as per Ed's drawing). Hold them on top of each other and feel that there is not much difference. Now stick them to each other with double-sided tape along the whole length and notice a massive difference in stiffness. Try only 3 spots of double-sided tape and see that it is weak again.

This experiment emphasises the need for all those screws bonding the two parts (plate + tube) of the z-slide together.
  #19  
Old Wed 09 April 2008, 06:45
domino11
Just call me: Heath
 
Cornwall, Ontario
Canada
Gerald,
Would using the VHB tape help at all between the plate and tube of the z slide along with the screws? I know of some applications that this tape has replaced welding. Or would the thickness be a problem?
  #20  
Old Wed 09 April 2008, 07:39
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
No, the VHB tape won't help if the screws are properly tightened. (If the screws are not tightened, then anything will help! )
  #21  
Old Mon 14 April 2008, 12:12
kwang90020
Just call me: krod
 
California
United States of America
If I use two guage plates as shown in the pic, would that strengthen the z axis?
Attached Images
File Type: jpg mm (3).jpg (26.5 KB, 325 views)
  #22  
Old Mon 14 April 2008, 12:59
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Yes, it will be a stiffer slide.


I am closing this thread now.
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