Comments on my first attempt at a design (if you would)

[lukekjackson]

JAZZCNC, thanks

Widen the Y-axis rail spacing, you have plenty of space so use it. Also, this will allow easier access to the bearings bolts, the way you show it now looks like you the X-axis bearings will block access to the Y-axis bearing bolts.? - One iteration actually has these wider, not sure why i closed them up but i will move them back out,. Nice easy win there

This brings me to one thing I've been struggling with, the X axis has a lot of overhang. Using 25mm HIWINS with the block spaced 36mm apart does anyone know what the max overhang should be? Obviously the longer i make the table to more travel but there has to be a point where you lose rigidity



#2
The triangle plates at the rear I would move to the outer edges and fasten to the side of the columns, this will give a wider footprint, I'd also think about adding some lateral bracing to add sideways support. - Again another easy win. the ridiculous reason they are there is that the column came with holes tapped for the Z rack so i used these. it will actually be far easiest fixing them to the sides as i don't have to drill through the depth off the gusset plate,. Should definitely have been doing it your way in the beginning

Like muzzer mentioned the column risers look a bit flimsy so maybe beef these up. - Still surprised but you all seem to agree. this may be one to do when i have the mill working so i can skim the sop of some stock to flatten it out. Either that or i could fit letteral section in between the risers to strengthen the riser design

#3
It's been said but worth mentioning again because it's a Biggy. The Z-axis plate needs to be double the height and the spindle housing needs to be wider.
Also, the spindle motor plate needs supporting or the vibrations will kill the spindle bearings and vibrate on the machine general. - Ill pick these up on the next revision and repost a snapshot of it

Good luck.- Cheers, Ill need it

[John11668]

I wonder why you felt you needed such column height relative to your X and Y dimensions . What height of components do you envisage .

One of the most difficult machining tasks I remember from my early days in industry, was a tall titanium columnar forging which needed double curvature machining onto its top face. It cost a fortune in fixtures to fix and support it and the machining had to be extremely slow to keep cutting forces within bounds. It was done on the table of a triple headed Bridgeport copy mill ( pre cnc days) So machining time for the op was 300 hrs although we could produce 3 in that time, and we needed a pair for each airframe. Prima Donnae in the drawing office would not consider a design change which could have cut the time to a tenth.

The point here is that columnar components are seldom machined standing upright on the table so large throat clearance is seldom needed .
It detracts from rigidity in the column and also in the component , so you get a double dose of flex in response to the cutting forces .

What is the maximum height of your proposed component? Work from that taking into account the Z positions for clearance and depths of machining operations , spindle retraction etc . Tall components will need to be braced from the table so add to the need for table width and extra rigidity.

Looking at your design I see an X / Y table sitting on a flat base . You could save yourself some time by buying one of those and adding the ball screws and motors which was the route I chose to take. OK so mine may not be the prettiest in the world but I wanted to get quickly to the eletronic/ software stage and start to play.

Hanermo mentioned Deckel Aciera and Shaublin , all good examples of well designed column mills from which design lessons can be learned .
I used my Deckel FP1 as a base , but as they say on the BBC , other makes are available . You will not find anything more rigid upon which to base your build .

My project is here http://www.mycncuk.com/threads/13746...802#post117802

[lukekjackson]

hanermo2, Cheers

The z axis ratios are way wrong -- as others have said.

So if you have 600 height you should have 300-400 mm width and depth for best results, and not less than about 250-300 in each dimension. - Column Width at present is 270, Y to the furthest point of the gusset from the face of the column is 190mm
It´s dirt cheap , relatively.
All modern machines use similar methods with large sections and relatively thin walls around 10 mm.

I think I'm a but stuck with this as i already have the surface plate. I thought as the column was off an SX3 and i was using two size to side it would be far stiffer in the Y axis then the gusset plates would help the Y. I will change the gussets as advised by Jazz and may put some in the x axis but I've run out of depth in Y to stiffen it up any more, i don't want to move the column forward as i will loose Y travel.

What would the consensus be, move column forward and loose travel but stiffen the Y or not?

[lukekjackson]

John11668.

I wonder why you felt you needed such column height relative to your X and Y dimensions . What height of components do you envisage .

In short i didn't really decide on relative dims, i wanted to upgrade the Z on my CMD10 so bought a a X3 column which has far better proportions than the stock CMD. While tapping for the linear rail fixings messed up a couple of holes and snapped a tap in 1 so i bought another one. Then as i had 2, I thought if I fix them side by side its even more rigid. once i modelled this up it looked ridiculous in comparison the the X/Y table (already replaced from the original CMD10 one). so whats the the obvious next step, start on a new X/Y of course. It is a slight case of scope creep from the original intent


What is the maximum height of your proposed component? Work from that taking into account the Z positions for clearance and depths of machining operations , spindle retraction etc . Tall components will need to be braced from the table so add to the need for table width and extra rigidity. - I have been thinking about this and you are correct i cant see myself ever needing to mill the top of something 400mm + high in a serious way. What i could imagine though would be drilling or flattening an edge. I'm effectively thinking i may mill up to a couple hundred mill high and only drill above that

Would it be worth losing the risers, i just didn't like the idea of having unusable rail under the lowest point the head can reach. and if the highest point of the Z axis is rarely gong to be used or only used for drilling does it matter if when using that section it is not as ridged as ideal?

Looking at your design I see an X / Y table sitting on a flat base . You could save yourself some time by buying one of those and adding the ball screws and motors which was the route I chose to take. OK so mine may not be the prettiest in the world but I wanted to get quickly to the eletronic/ software stage and start to play. - that was my initial plan and i did buy a larger X/Y table, i Want to add linear rails and ball screws though and when i though about what i would have to do to the X/Y, and how i would do it only having access to the CMD10 to do the work it seemed like it would be more effective to use a surface plate and ground flat stock to build one. It would save me a lot of machining squaring things up in theory. I have no doubt i will live to regret that.

Hanermo mentioned Deckel Aciera and Shaublin , all good examples of well designed column mills from which design lessons can be learned .
I used my Deckel FP1 as a base , but as they say on the BBC , other makes are available . You will not find anything more rigid upon which to base your build - Just had a look at the FP1, that does look look like a solid lump. To give me some frame of reference what depth and speed of cut would this sort of machine regularly make in steel. the Belt drive I've included will take the spindle speed up to 10K RPM so i'm of hoping to use smaller cutters at higher speeds to make up for the lack or rigidity of not having a big cast base

[John11668]

These mills are toolroom mills http://www.lathes.co.uk/deckel/page5.html
Shows the sort of work they normally are bought for . Lots of clones including Alexander in UK https://www.ebay.co.uk/itm/164561029...m=164561029251
and optional high speed head will go up to 6K rpm but lots of scope for bigger cutters /

These are pricey but lots of other cheaper options Harrison, Viceroy, Elliot to do similar with

[lukekjackson]

I'm back with my updated "design".

I think I've taken most of the advice on board, the glaring omission in the "spindly" legs. My problem with this is the ability to flatten a solid block of steel that size. I've added another leg, actually due to the fixing points clashing with the webs under the Surface plate, but it cant hurt rigidity. Once its up and running i may revisit this.

General Overview


Increased Z Carriage
Head Strengthened Laterally
Pully Drive Fixed down to the head at the back


Column Gusset plates moved


Y Axis Linear bearings widened


I've also lost the T=slotted table and decided to go with a fixture plate type setup tapped for 6mm bolts and drilled and reamed for 6mm dowels for alignment. The table has got longer though which makes the overhang a bit of a worry.



My reading of the HIWIN Data sheet for the HGH25 say dynamic moment My is 240Nm equates to c. 24Kg at a meter for one block, my total distance from block to furthest point is c.0.5m meaning 48kg is required to hit the max, there are 2 rails, so 96Kg and that doesn't account for the blocks being in pairs per rail, which you would assume would have a fairly large impact torque applied.

So if i understand the Data i could put over 100kg on the table at full extension and still be in the limit. If that is the case i have no worries but it just looks wrong. Could someone check my logic.



The last lot of comments were a big help so any more would be appreciated.

I'm also looking at a frame and enclosure so will be back with more at some point

Cheers,

Luke

[John11668]

Starting to look almost like a Deckel
So cant be bad !