12" Z Axis

[kubotaman]

Okay please tell me does anyone wish they had bought the 12" Z axis? If you do have one, have you noticed that it has a tendency to flex while using it and if so does it pose a problem? Is it worth the extra money to buy? I have just "posted" the thread of "prices" and am trying to get all my information before ordering. Thanks!

[cabnet636]

a deep z is basically a rare thing and is used by those who would be doing say "art work sculpture" would be a good example, if it is somthing you are not sure of in this case you may never notice, it has a specialized purpose. i am sure others have a take on this as well

jim

[pezsez]

Im only a "botter" for a few months now--but from what I have seen ----unless you had a specific use for such a big Z, the only time it would make ay sense is if you had a multi axis machine (5+) so the bit could get in to all the nooks and cranny's

PEZ

[khalid]

In future if u have a vision to do Rotary 4th-axis work (or to install Indexer)..This high Z-will be benefit u then..Unless no need to have 12" Z-travel...

In my Machine I deliberately kept 8" of Z-axis... This will be enough for my Indexer work.. The more u increase the height of Z-axis , the greater the flex u will get, the poorer the quality of the cut (This will not true for rotary work, bcas the Z-axis will work on maximum height)..

[cabnet636]

i will say this i needed 8 inches one time to carve a letter into the marking post of a cemem tary, it came in real handy for that!1

jim

[drodda]

I bought the 12" Z axis based on the fact that if you wanted to cut clear through a 4 x 4 you would need 4" of clearance for the wood and 4.5" of clearance for the bit that is long enough to go all the way through the wood.

With that said I have only had maybe three times when I needed this situation and I have fought the flex it gives way too many times to count. My machine is a PRT-Alpha though. I finally glued down 10 sheets of mdf to the table to reduce the flex. This really improved my edge on hardwood when cut. The indexer was also a reason I wanted the 12" Z but have never gotten time to buy and play with the indexer.

In summary when I buy another it will not have a large Z axis. The money and other issues would deter this for another purchase.

-D

[khalid]

If u have to cut 4 x 4 daily on ur bot, then its okay to have 12" z-axis... but if u do the job once in a blue moon then its not good to have it...
Normally such high thickness jobs comes some times in life...

I have 6" (~150mm) of Z-height in my MDF machine that can do 3" dia workpiece indexing jobs without any trouble...IMHO usually woodworker do indexing jobs not more than 4" thickness of stock material...

If u are intending to do more height jobs then u can buy 12" z-height, else save money and buy 8" or 6" z-height... i will advice u to get 8"....

[kubotaman]

So it is possible to buy less in the z axis height? I didn't know that. I will ask. One of my first jobs is in fact to do stringers that are a full 4" in height. I have red cedar that I have milled to be the stair case to a home I am building for the wife and I. That is one of the reasons for the 12" z axis. Dave Rodda, where does the z axis flex? Can it be braced in some way to not flex. I suspect that it does flex when it is in the lowest position. In other words when nearer the table. Am I correct? Is it a case of too fast of a feed or too fast of a speed when starting to mill the material?

[cnc_works]

It is simple physics, Daryl. Put a 1/4" diameter 12" long rod in your drill press. Push on it 2" down from the chuck...using the same pressure, push on it 12" down from the chuck. Any flex in your spindle/router is magnified in the same manner. You can overcome some of it by slowing down feeds, but it will never completely go away.

That being said, if you need it, you need it and you learn how to make the most of whatever you have.

Personally, I would forgo that much Z unless it was going to make me big money.

Donn

[Gary Campbell]

Daryl...
The full size Bots that are shipping now have around 8 1/2" clearance between a 2 layer spoilboard and the collet nut. We have recently cut full 4" Aformosia with this configuration. There were a few concessions to do this. There was no room for the dust foot. We also had to edit files to keep the safe Z height to .25" Small concessions in my mind.

We have a 2007 PRSa that originally shipped with more Z clearance. We have replaced the original geometry and mechanics that resulted in that extra clearance in an effort to reduce the flex.

Even tho the models shipping now are more robust as far as the Z flex goes, unless you have a specific, ongoing, light duty use (such as foam or soft material 3D cutting)that requires the extra Z height, do not order a machine with that configuration. (IMHO)

We have spent $2500 in upgrades to lower our Z height (among other features) and would spend another $1000 to lower it further, as I believe that it improves the machines performance. This opinion is based on professional full time use, cutting sheet goods aggressively , rather than hobbyist or 3D use.

Others have raised their tables to accomplish the same.
Gary

[khalid]

IMHO We can make DIY bearing supports when the Z works in it minimum height positions (lower Z-heights)...this will reduce (eliminate) the Flex..

Shopbots are well-engineered, and designers of it must think of z-flex is such situations... During the designing phase of my second machine, we even calculated the Center of gravity of the Z-axis mounting plates with and without holding the router..Good design make difference and I know Shopbot manufacturers and designers must have cater for the high flex issues during the design phases of it...

In the High Z, u must use sharpened bits otherwise the flex will be exaggerated and will show in the cut quality of ur workpiece...

[khalid]

In the 12" Z, sometimes u have to use longer tool bits in case of your Stock thickness is very high and u have to cut some locations to the minimum lower thicknesses.. the longer tool bits have runout issues and flex itself... So u can't use them efficiently for harder material...

P.S: I neither used nor seen Professional machines... All my thoughts are the results of experiences with my DIY machines... so don't influence on my opinions...Listen to the real shopbotters in this forum...

Regards

[kubotaman]

Okay, It looks like most of you have voted against me purchasing the 12" axis. If I have to cut 4" material with a 4" bit then I would need no less than 8" axis. If that is true does the "standard" axis permit this? Is it possible to cut with a 2" bit then install a 4" bit to finish the cut? That way a person would not need to be at the highest z axis to start. You could start at say 7" with the 2" bit, cut down 2" in say 1/4" incriments, install the 4" bit and finish the cut. Have I got it wrong? What is the clearance on the PRS Alpha now being sold, with the 6" z axis. Is it more than 6"? I completely understand a longer bit will flex but what flexes as far as the 12" axis? I have never seen one let alone a ShopBot!

[khalid]

Daryl... again sorry for interuption...

Depends upon many factors;)...

If u have to pocket a small area in the big stock...u will pocket upto 2" with smaller tool...Sounds Okay;)
Now u have to change the tool.. I think for changing the tool the bot will command the move to Home position.. Now its also seems Okay..

After changing the tool with lengthy tool..now when u move back to that pocket location the tool will strike the outside walls of pocket
...just imagine...

Some times this happen..

Regards

[kubotaman]

Good point! Then what heigth z-axis is available. All the material that I have read is 6" or 12" Are there heights in between?

[beacon14]

However if you are not pocketing, as in stringers, you can (carefully!) plan your toolpath to only approach the workpiece from the side, say at a starting depth of 1/4" or 1/2" (1/2" in cedar should be no problem). Then no need to raise the bit above the workpiece at all.


6834

I've been using one Shopbot or another for nine years, both with 6" Z axis, and so far I can't recall anything that was too tall for me to cut.

[khalid]

Daryl... I don't know
May be some one from Shopbot management plunge into the matter....

Regards

[khalid]

David... Ohhh man..what are u cutting at ur shopbot
... I think u are levelling the wood... if this is pocketing operation then its a great waste of costly wood

[drodda]

You are correct about the flex coming as the bot is at it's Lowest point. However if you are cutting 3/4" ply with a 12" Z axis the bot will be used at this lowest point for most of it's cutting. That is why I say buy the shortest Z you can live with.

Unlike most who buy a bot for hobby use I actually still use my bot for the very things I bought it for. So as I mentioned I have only needed the height a few times in over three years. But when I needed it I had it there to use. I've learned to live with the flex issues.

-D

[kubotaman]

Dave, since it sounds like you have the 12" ShopBot and you say that it does have some flex, at it's lowest point, am I to assume that the flex is in the carriage holding the spindle? Do you use a router or spindle? I am planing to purchase a spindle if that makes any difference.Do you see a way of improving it?

[beacon14]

Khalid,

That was a 100 year old piece of reclaimed heart pine, we had to machine a 2" deep recess for it to fit over an existing mantle.

Even after being indoors for 100 years it was practically dripping wet inside. The whole time it was cutting it threw off wet, sticky chips which welded themselves to the rails and wheels. What a mess. No more heart pine on my Shopbot.

[khalid]

David... I really like the texture of that Pine wood... Its 100 years old and still not seasoned
..amazing...

Hmm... I will be grateful if u can share the picture of the mental u made out of it (u can paste a link or PM me i really want to see the finished product)... Very nice looking shopbot and very nice texture of pine...

Sorry Daryl i went offtopic...I have so much attachment to wooden stuff that its hardly control to express my feelings..

Regards

[drodda]

I have a 2005 PRT-Alpha. I don't know if they have improved this on the PRS-Alpha or not. I use a router but the flex is in the carriage. I spent the first two years working on getting rid of the flex and the last learning to live with it. I was told of this before I bought my machine from shopbot. So it was a tradeoff I decided to take at the time. Looking back I would have a 6" Z and built an area just off the table to have a lower platform that would allow a larger piece to be secured at table height.

[hespj]

Daryl, I have 12" Z on a 2005 PRT Alpha. I'm not sure if the current config would allow as much flex, but mine does have flex (in X direction - the Z slide is not as stiff in the X direction).

Most of the time a 6" box sits on the table (screwed down) to reduce Z to 6". End of problem. I treat the top of this box as my spoilboard.

Do I take away the box and use the 12" Z much? No, but I've probably made more money with the Shopbot in those short 12" times than all the 6" times put together. I can work round the flex at these 12" times. 12" Z means I'm cutting 3D rather than 2D, and my 3D work method demands roughing cuts followed by shallow clean up cuts. The shallow clean up cuts don't suffer deflection so much. Deflection seems to be due to the rotation of large cutters dragging the Z slide sideways.

John

[Gary Campbell]

Daryl..
If you notice in my post above, the machines that are shipping at present have approx. 8 1/2" from the collet to a 2 layer table. Your table construction could gain you an inch. Mine is 1" plus 3/4 for Plenum, plus 3/4 for spoilboard. Put down a sheet of 1/2" aluminum and you have almost 10"
Gary

[beacon14]

Sorry, Khalid, I only did the machining for the fellow who saws my logs on occasion, then never saw the piece again. Next time I see him I'll ask him if he got any pictures.

[kubotaman]

Gary Campbell, I called ShopBot today and asked what my choices were as far as Z height. I was told that they only come with 6" or 12", and nothing else. I then asked what the clearance was between the collet nut and the table for the 6", which would be two 3/4" thick sheets. I was told it would be a total of 6". How were you able to raise yours to 8 1/2"?

[kubotaman]

I have another thought. I found out from ShopBot that they get their heigth for the Z axis by stacking another side rail on top of the first rail that comes with the 6" axis and also give you a longer mount on the Z axis for a total of 12" axis. Since I will very seldom use the heigth of 12", is it possible to install heavy wall square tubing on top of the first 6" rail to give me more heigth? If I were to install 3" or 4" it would then enable me to do the project I have in mind. If I needed to be able to cut to the table itself I could buy the longer z axis mount from ShopBot. What is you guy's opinion? Will this work?

[Brady Watson]

A standard Z axis will get you about 8" give or take. A 12" Z will get you a little over 12" of travel.

If you are not cutting foam day in & day out, or are not doing 4th axis/indexer type work day in & day out, then skip the 12" Z. It is very useful for someone who needs it, but a hinderance if you don't - If you cut 3/4" MDF every day for cabinet parts, then it isn't a good choice for you.

Choose the right tool for the job at hand. ShopBots are VERY versatile machines & easily upgraded/customized using either factory parts or your own ingenuity.

-B