一种新型8020 extrusion直线运动系统

qinsdau

MacMarty     Join Date: Feb 2006
Location: USA
Posts: 17


Thanks for the tips, Ahren. Now I'm going to show off my total newbie-ness and risk being flamed for what I am sure is a frequent and divisive question.

If one were to use the hoped-for longer carriages to support the gantry, would it be at all reasonable to use this rig for drilling holes in 6061 aluminum plate? Or to put a nice square finished end on a piece of 80-20 extrusion? My thought is to keep the downward force within the area encompassed by the longer carriages.

I know that this is all about cnc=ROUTER=parts, and I know that there are probably some feeds-n-speeds issues involved, but is such service realistic, or a total misuse of tooling?

qinsdau

MacMarty,

As you implied in your post, this is not a straightforward question to answer. Depending on what tooling you are using, you could be OK, or you could be in a heap of trouble! Typically, aluminum cutting speeds are much lower than wood for a given diameter cutter. A simplistic but easy to use formula is here:

http://www.stanford.edu/group/prl/cg...Cutting_speeds

For squaring up extrusion, you'll want a long depth of cut (1.75" or so), which probably means at least a 1/2" cutter, which means around 2400 RPM with this formula -- most routers don't go this low. But let's say you use a spindle instead Your biggest nemesis with a tool this long will be chatter, which is really best eliminated by a stiff, heavy machine. If you don't have any really long lever arms, the bearings should be able to take it, but you'll want something suitably sturdy for them to ride on, like a welded steel frame. An aluminum machine may not suit your purposes here.

My $0.02,

Ahren

qinsdau

Great blocks Ahren!

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I have been working for machine builders for the last 15 years and have spent a good deal of my free time building or assisting others in router projects. These are by far the best items I have seen for homemade equipment.
Some observations -
-Choose a quality steel rail to realize the full potential of these blocks if you need the accuracy. I put mine on some ground 1018. Let's just say I am not shopping for thomson pillow blocks on Ebay anymore!
-Using inexpensive steel for the rails may result in a rail that is not entirely straight. If two two-wheel blocks are used on the top of a y-axis, all of the wheels may not touch all of the time. Not an issue for those with a light weight z-axis.
-Last, the adjustment wheel takes a little care not to preload the bearing too much. Keep in mind that the thickness of the steel rail may vary. I damaged some bearings (no fault of the blocks) by not checking the thickness for the full range of travel.
Thanks Ahren - I am ordering more tonight.

BobW

qinsdau

Bob,

Glad to know the carriages are working out for you. Let me know if you need some spare bearings (I obviously have a lot of them , and I can throw a few in with your additional order tonight free of charge.

Best regards,

Ahren

qinsdau

MacMarty     Join Date: Feb 2006
Location: USA
Posts: 17


Other "wrapped gantry" routers?

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Hello, All -

Ahren, thanks for your comments regarding the suitability (or not  ) of using this router scheme for a mill. I've long understood the difference between "can" and "should" in other contexts, and I now conclude that I should NOT abuse this tool.

So, I'm ready to jump in, once I get my head around the frame/table design a little more. I understand what I see in your axis-drive illustration, and I think I understand what I see in what I'll call your "wraparound gantry" scheme. Obviously the material-holding table goes through the center of the gantry, but the part that escapes me (so far) is how/where the X axis-drive is placed and attached, relative to the gantry and table.

I've browsed around the Zone to see if I could find a similar arrangement, and I quickly realize I could wander in this wealth of resources for quite a while! Can you point me to any specific comparable builds that are posted here or elsewhere? (Does not have to be 80-20, just needs to show me how the gantry, table, and X axix-drive relate to each other.) Part of me suspects that putting the axis-drive under the material table would protect it from some dirt and bumping, but what do =I= know?!?! I'm just a happy and eager NOOB!!!

qinsdau

I would be down for some 8"ers if my current rails don't pan out.  Nice design I have thought of this concept and seen a few other variations on it over the years but yours is the first I have seen offered for sale. Well Done


Bo

qinsdau

harryn     Join Date: Apr 2007
Location: USA
Posts: 556


I looked at Mcmaster carr for 1/4 hardened, precision ground steel.

Material 4140, hardened precision ground steel
PN 89715K441

4 in wide, 6 ft long, 4140 in hardened condition, precision ground

Thickness tolerance = +/- 0.002 in
Flatness tolerance = +/- 0.030 in (in 6 ft), but 1/2 that in 18 in.
6 ft Price = $ 143. xx
18 in price = $ 43


I am just curious - it seems like abec 3 might be a better choice for bearings. Would you consider that as an offering ?

qinsdau

Harryn,

You could go with McMaster for steel, but they'll likely be quite expensive -- there are several links on my site to good sources of steel online. While ground flat will certainly give awesome accuracy, the more budget minded might be interested in regular 1018 (cold rolled) steel. The tolerances are still surprisingly good:

http://www.speedymetals.com/information/material26.html

As for the ABEC bearings, there's nothing to stop you from swapping them out (although you will need to drill a hole to get the doweled bearings out -- an oversight that will be corrected in future product runs). I had to make some trade-offs to keep the price around $20/carriage, and adding more expensive bearings (6 of them!) wouldn't have allowed that. The tighter tolerances don't actually buy you that much in terms of machine accuracy or load rating -- they mostly let you run the bearings longer and faster, and in this context they won't see anywhere near their max speed rating, so this isn't all that helpful. However, if you're set on "pimping" your carriages, the bearings are standard 8x7x22 skate bearings. VXB has some nice ABEC 7's on sale for $0.50 each if you buy in bulk:

http://www.vxb.com/page/bearings/PROD/8mm/Kit7604

If there's a lot of demand for higher accuracy bearings, I could offer them as an option. For now though, if anyone is interested in buying blocks without bearings, just let me know when you make your purchase -- I'll refund $1 for each carriage, and just give you the rest of the hardware.

Ahren

qinsdau

MacMarty,
Below is a conceptual picture of the "wrap around" configuration I mentioned earlier, whereby the whole table is surrounded by the gantry. This setup is potentially more resistant to racking due to the wider spread of the bearings. This model is really rough -- I wouldn't go with this configuration as shown, but it should give you an idea.
Note that both this and the previously shown configuration both lend themselves to driving the gantry under the table. This is a nice feature, as a) it can make use of my motor mounts and bearing mounts (OK, gratuitous plug, sorry), b) drives the axis in the center, cutting down on racking, and c) keeping the screw away from dust and debris, as you mentioned.
I would get a copy of sketchup and start drawing up some concepts for your machine. It's free, and models of my parts are available for download on the CAD page. Start playing around and posting your stuff on the zone for feedback. That's the best way to learn, and there's a very supportive community to help you through!

Best regards,

Ahren
www.cncrouterparts.com
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qinsdau

freecncplans     Join Date: Feb 2008
Location: USA
Posts: 2


I didn't see this posted anywhere, but would be nice to know.
Sean
FreeCNCPlans.com

                               
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qinsdau

Sean,

A good question. The standard bearing stack for the dimension you list is 0.508" (screw head + bearing + spacer). I can also offer a low profile spacer that reduces this to around 0.450" -- just make sure to ask for it when you order.

Best regards,

Ahren

qinsdau

Hi all,

Just FYI, I'll be in Europe next week, and since I won't be able to ship anything during that time, the store will be closed. The store should re-open when I get back on Feb 17th (with NEMA 23 motor mounts back in stock!)

Best regards,

Ahren

qinsdau

                               
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ABEC 7 Bearings Now Available for Linear Carriages
All,

After several requests, I now have ABEC 7 bearings available as part of my linear carriage offering. These ride even smoother than the originals, and they're a snazzy red color as well, for only a small increase in price ($2.25 per carriage). If you've already bought linear carriages from cncrouterparts.com, I don't want to leave you out in the cold, so you can upgrade for the same cost -- just email me from the contact page to make arrangements.

Thanks to all of you waiting on bearing blocks as well -- I will be releasing more soon, with a redesigned all-aluminum construction (no more rust spots on the covers), better bearing fits (only +0.001" over bearing OD) and small machined clearances to insure no rubbing on inner bearing races, even under heavy thrust loads. CAD pictures below, real parts to follow next week.

Lastly, there's a special surprise coming at the end of the month...

Thanks for your interest!

Ahren
www.cncrouterparts.com
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qinsdau

harryn     Join Date: Apr 2007
Location: USA
Posts: 556


Thanks for adding abec 7 bearing option - that is the path I will go.

I am thinking of adding a wiper - maybe UHMWPE or oil soaked felt to the end to keep chips out of the wheel / steel interface. It looks like there is not enough room to screw it to the ends ? I guess I should plan to mount the wiper to the plate that holds the rest of the axis parts ?

Suggestions ?

qinsdau

Harry,
If you want to add wipers, you could possibly use the tapped 3/8-16 hole that holds the dowel pins in place. There's nothing special about those set screws.

Otherwise, things near the ends of the carriages are a little tight -- I was trying to keep the bearing spacing as wide as possible. Mounting a brush to whatever the carriage is mounted to is probably your best bet.

Ahren

qinsdau

All, first cnczone build log using cncrouterparts linear carriages is here, and a beautiful job of it as well:

http://www.cnczone.com/forums/showthread.php?t=53316

Way to go Greg!

Ahren

qinsdau

Ok, I just ordered 14 of the ABEC 7 version for my DIY build. (more will be needed, but that is the budget )

http://www.cnczone.com/forums/showth...298#post421298

If you knew how much I ponder these sorts of things, you would be impressed. In the end, I picked them over redi rail and frelon sliding parts from Pacific Bearings.

qinsdau

Harry,

Thanks for the order -- just packed it up, and it should go out tomorrow. I think you'll be much happier with a rolling solution over frelon (at least a factor of 10 less dynamic friction, making binding nearly impossible). I hope they exceed your expectations. I'll be following your build to see how it goes!

You did nearly clean out my stock of carriages, although I started some more before you placed your order. I have 6 left, and plenty more should be available in 2 weeks. For those of you waiting on bearing blocks, again I'm sorry for the delay. I'm hoping to have a few ready for sale next week.

Best regards,

Ahren

qinsdau

rail width?

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Hi, Ahren -

I've started construction of my table, using horizontal rails and the wraparound gantry that you illustrated in post #31. One thing that I can't quite sort out from looking at that JPG is the -width- of the Y rail. ("height" in that orientation.) My graph-paper sketches tell me that it needs to be perhaps 4.5" wide in order to mount it to a 1530 beam, and still have clearance for the bearings and bolts. Am I correct, or am I being overly conservative? What is the width of that rail in your sketch?

Yes, I will start my build log soon -

- Marty

qinsdau

#42          03-19-2008, 03:53 PM  
ahren     Join Date: Feb 2004
Location: USA
Posts: 270


Marty,

I just looked, and it appears I had a small error in the CAD file posted on my website. The error is in the position of the two bearings in the slots -- the model shows these are 0.394" from the edge, while in actuality they are 0.375" away. I will fix this as soon as I return home from Europe (travelling this week).

What this means for you is that there is actually a little more clearance, since the bearings in the slots ride "higher" with respect to the bolts. There is about 0.015" of clearance on either side with the standard arrangement on a 4" wide rail. If this is too tight for you, I have some lower profile washers that can get you more room (0.031" thick instead of 0.093"), so an extra 1/16" on either side -- just email me and I can send them out to you.

A 4.5" rail will certainly work, but is likely harder to get. Also, make sure that if you get a 4.5" rail, that you confirm it was rolled to this dimension, and not cut from 1/4" plate.

Looking forward to your build!

Ahren