Design Questions

[SixOfOne]

After about 6 years of lurking I think I'm about to take the plunge (I hope nothing bites me in the a$$ this time). I’m in the design phase again due to so many advancements in DIY builds. I’m probably going with something like the 8020, CNCRouterParts, R&P equipment and I have hit a few snags in my design that require input.

1. CRP.com has the High Z plate which moves the router mount from the plate to the 8020.
Q: Does the RM-PC892 Porter Cable 690 & 892 Mount from K2 mount to 8020? If not are there any suppliers of a mount for a router that does? (a sketchup model of this part would be helpful)

2. Since a 3060 extrusion is so expensive I was thinking of a welded steel gantry (still using CRP’s Rail system) so I would plan on using at least a 2” x 6” rectangular tube for the long and 2.5" x 2.5 uprights.
Q: What would be a suitable wall thickness for a 5ft wide gantry and the uprights? Would a 2x6 & 2.5sq tube be enough?

I hope tomorrow to get my sketch-up plans and a quick BOM for people to look at and maybe tell me where I might have issues.

Edit: thought of another question…
When I look at some build photos all I see is a anti-backlash coupler & 2 collars on their Z. Are people using the thrust bearings right on the acme? Or are they using a collar to connect the drill rod to the acme? I assumed this would be a "no no" due to the threads.

[DonFrambach]

Originally Posted by SixOfOne 1. CRP.com has the High Z plate which moves the router mount from the plate to the 8020. Q: Does the RM-PC892 Porter Cable 690 & 892 Mount from K2 mount to 8020? If not are there any suppliers of a mount for a router that does? (a sketchup model of this part would be helpful)

The holes for the K2 mounts will not line up with the slots of 15 series 8020 extrusions. However, it's easy to make an adapter. I drilled and tapped more holes than necessary in a piece of Fortel aluminum so I could attach a number of different spindle mounts to my 8020 extrusion (including K2 mounts). Here's a photo:

[DonFrambach]

Originally Posted by SixOfOne When I look at some build photos all I see is a anti-backlash coupler & 2 collars on their Z. Are people using the thrust bearings right on the acme? Or are they using a collar to connect the drill rod to the acme? I assumed this would be a "no no" due to the threads.

I have built all three of my axis without using drill rod using collars from CNCRouterParts.com on two axis and, for clearance reasons, parts from DumpsterCNC.com on the other. I've had no problems. Here's a photo of the axis using DumpsterCNC.com collars.

[SixOfOne]

Well that will save me some $$ and some space.
Zero Backlash Helical Shaft Coupler
5 Start 10 thread/in 1/2″ Acme Rod
1/2" Shaft Collar x2
1/2" Needle Thrust Bearing and Washers x2
Bearing Block and Cover
Low Profile Bearing Block
I just assumed thrust washers and collars on the threads was going to cause harm to the screw during operation. If your all doing it and not having issues then its good enough for me.

What is the difference (besides the obvious) between:
5 Start 10 thread/in 1/2″ Acme Rod -3ft:
Plain 1018 Carbon Steel 99030A304 $28.75
Black-Oxide Heat-Treated 4140 Alloy Steel 98940A627 $43.45
Is there a reason to use the most expensive one?

Now to decide on a Z travel distance, so I can decide on gantry height. I would like to be able to carve 7” deep into wood without the router or mount hitting the work piece. This means I would need a 7-8” bit. Plus that much travel. Any suggestions on a good wood bit that’s 8” (not counting shank). I guess once I know the prices of this type of bit I can decide how upset I’ll be having to cut models in half to mill 4`ish” at a time, then glue together.

While I’m asking about bits and Z axis stuff I might as well ask what do you all think is a reasonable Z height? Am I over reaching?

[SixOfOne]

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[SixOfOne]

I've never ordered from Grizzly before, nor built anything that needed CNC accuracy. I put together a list tools I'm thinking of grabbing before I build the CNC. Only thing that worries me is quality of this stuff. I know decent measurement tools can become my entire CNC budget quickly, but will this stuff do?

I have stuff like framing quick squares (triangle), 4' & 6' beam level (bubble), tape measures galore, 6" or 8" Digital Caliper, magnetic torpedo laser level, drywall squares, carpenter squares but nothing close to 0.001" accurate

From the below list what would you keep? what would you add?

G9849 - Magnetic Base/Dial Indicator Combo - President's Special - $22.75
T23018 - 0-4" Digital Snap Depth Gauge and Indicator - $15.99
Do the above perform the same function? grizzly has soooo many different indicators I don't know which one to chose (digital being a plus because easier to read but a neg when the damn bats go flat)

I couldn't find a 6' alum straight edge on grizzly which I think would be nice to have for this project, figured I would just order or pick up a ground Al flat-bar...
H2993 - 4 pc. Machinist's Square Set - $17.75
H8130 - 32" Digital Laser Level - $59.95
T23019 - 8" Digital Protractor with Rule Blade - $19.99

[stewi]

I'm missing the Acme screw nuts in your list of parts.
If you go with backlash free, spring loaded nuts, than here are some $$$ to spend. 1/2 - 10 Left Hand Acme Lead Screws & Nuts for Power Transmission - Roton Products, Inc.
McMaster is convenient, but not inexpensive.

[SixOfOne]

Originally Posted by stewi I'm missing the Acme screw nuts in your list of parts. If you go with backlash free, spring loaded nuts, than here are some $$$ to spend. 1/2 - 10 Left Hand Acme Lead Screws & Nuts for Power Transmission - Roton Products, Inc. McMaster is convenient, but not inexpensive.

Oops! TY Stewi, Yeah that part would be helpful to add

I'm more then likely going with the "1/2-10 ACME Nut, 5 Start" from CNCRouterParts. My machine will be based on their CRP4848 machine. Once they get their plans updated on the site (they are there now "revA" but locked so I can't take measurements from the models) I'm hoping to get my plans finalized.. Still haven't made a decision on what I want for Z height/travel which might make the Gantry Riser Set they sell useless to me unless I went with a raised gantry/dropped table setup and that just seems like a waste of materials and more room for mistakes.

On another note, I did find in storage a massive solid wood desk from the 60-70's. UGLY AS SIN, covered in whats got to be 50 layers of probably lead paint (yummy, chips anyone?). It appears to be a solid table to put the machine on except for the fact that I will need at least 4.5' x 4.5' and the top is 5' 5" x 3' so I will need to add 1.5' to the back of it some how. It should be stout enough, it took 2 cans of spinach to move it Its a shame I wont be happy with a 4' x 2' machine cause it would be perfect on this desk.

[jsheerin]

I do my thrust bearings the same way as Don, right on the screw. My only suggestion would be to take the inner washers of the thrust bearings, the ones that bear against the bearing blocks, and glue them to the bearing blocks out at the edges so they are centered over the screw and can't slide around. I had an issue where those washers were grinding a groove in one of my screws. I held the washer against the block with the screw going vertically through it and put a few dabs of super glue around the edge of the washer. That's been working for a few years now.

I've been using the bare steel acme screws and haven't had any problems with them.

[SixOfOne]

Originally Posted by jsheerin I do my thrust bearings the same way as Don, right on the screw. My only suggestion would be to take the inner washers of the thrust bearings, the ones that bear against the bearing blocks, and glue them to the bearing blocks out at the edges so they are centered over the screw and can't slide around. I had an issue where those washers were grinding a groove in one of my screws. I held the washer against the block with the screw going vertically through it and put a few dabs of super glue around the edge of the washer. That's been working for a few years now. I've been using the bare steel acme screws and haven't had any problems with them.

Yeah, chatter is what I was worried about I didn't even think of it grinding the screw (I figured the thrust bearings would be beat to hell and the screw be harmed by the frags getting in the threads). Super glue sounds like a great plan to me, TY.

[SixOfOne]

Well I'm getting somewhere

I still need to make up a BOM and start pricing parts but I think this design will be the most flexible/cost effective for me. (see pics)

I used Ahrens welded steel table design for 2 reasons..
1. Cheaper then all those alum parts & hardware (I think anyway, still haven't priced)
2. Gives me more Z which I will explain my (warped) thought process.

The machine is very much like CNCRP4848 but a little bit exaggerated. I might be wrong (sure someone will correct me if I am) but Ahren has 49.5" x 49.5" with the router motor body/mount hovering over the rails. In order for me to get the Z height I wanted I had to get the Z rail, router mount & router body inside the rails which added to the width (3.5"). My garage isn't big enough for 4' x 4' so why not.

Now my reasons for this high Z travel..
1. I have wanted a plasma table for a very long time, just never had a need for one. (I don't even have the cutter yet) With the extra height I think I can make a water table & bed that will sit on top the wood bed. Cons to this are the over extension of the Z when milling/routing. If it becomes a problem I'll build a box on top the table (MDF is cheap) maybe a vac table even.

2. I wanted allot of room for a rotary axis

Opinions would be appreciated & thanks!!