[thebluedirt]

Hi, everyone:

I'm building a small cnc machine, planning on using ebay linear bearings, and acme threaded rod for the lead screws.

Since i have a bunch of them on hand, I'm planning on using 6208 skate bearings for the leadscrews.

The skate bearings have an OD of 22mm. Does anyone know of a source of cheap bearing blocks to hold the bearings? Ideally, i'm looking for a 'pillow block' kind of mount, though even a regular block with holes for screws would work well.

My thought is to load two against each other to remove play. I know they will not be as good as a good set of AC bearings, but since I have them on hand...

anyone have ideas? I could make them with a cnc if I had a cnc I am sure I cannot be the first to need to mount some 6208's without the abililty to bore a precise 22mm hole...

Thanks in advance for ideas.....

[ger21]

If you have a drill press, you can buy a 22mm forstner bit. CMT makes them, they're about $15. I've made some blocks from phenolic material I had on hand.

[GreenvilleDave]

Hi, thanks!

that was me below asking the question-- I've switched userids.

I ended up taking the advice about the forstner bit, but then kind of did some 'yak shaving' and took the opportunity to play with RTV silicon. I posted the results here:

http://www.cnczone.com/forums/showthread.php?t=72436

[cnccutter]

"If you have a drill press, you can buy a 22mm forstner bit. CMT makes them, they're about $15. I've made some blocks from phenolic material I had on hand.
__________________
Gerry"

Gerry, how did the phenolic bearing blocks hold up? I was planning on making some...

[ahren]

Are you planning on turning the ACME rods down to 8 mm in diameter? That might negate a lot of the cost/hassle savings from re-using your bearings. With a half inch bearing, you can sandwich each side with a thrust bearing to hold the screws, and let the screw float in the radial bearing to avoid excessive axial loads to it. You can see an example of this on the "parts" page of my website.

That being said, I like your mold! Your parts definitely look good, and it's a nice way to make things if you don't have a CNC machine at your disposal.

Best regards,

Ahren
www.cncrouterparts.com

[GreenvilleDave]

Hi, ahren:

Thanks for the reply. Yes, I found my way to your website-- your parts collection is nice.

Yes, my plan was to either turn the acme down to 8mm, or ( perhaps initially ) to use 5/16-18 threaded rod, which fits into the skate bearings just right.

[ahren]

Dave,

If it's in your budget, I'd definitely go ACME -- all thread makes a pretty crappy lead screw. Additionally, while 5/16 "fits", it's probably at least 0.004" undersized. 8mm = 0.316", 5/16=0.312", and usually a screws major diameter is smaller than the stated size. This is a pretty poor fit for a bearing, and could lead to whip in your axis at even a moderate speed.

Best regards,

Ahren
www.cncrouterparts.com

[GreenvilleDave]

Thanks for the info.

You make a good point about the tolerance on the allthread.

I've seen your bearing blocks in your store. Does the bearing block include the price of the 1/2" ID bearing?

Also, i'm curious, what do you see as the typical cost for those bearings?

I think you are right about acme vs allthread, but what's attractive is the per-piece price of skate bearings, @ < $1 per piece its hard to beat.

[LeeWay]

I used a combination of flange bearings and pillow blocks on my router.
I didn't use thrust bearings on it. I should have though. If the end play gets to be to much, I will replace those and install thrust bearings as well.
This is how I did my new lathe, except I used rolled ball screws with double nuts.
Very little backlash and no end play that is measurable.
Thrust bearings take up very little room and are pretty cheap. Same with flange bearings.

[ahren]

Dave,
Yes, my bearing blocks include the cost of a 1/2" bearing. They're only about $2 from VXB if you buy 10 at a time, but I added them to the assembly to save people an extra order and shipping charge.

Best regards,

Ahren
www.cncrouterparts.com

[GreenvilleDave]

i think your decision to add them is wise-- most who want the blocks would need the bearings too.

do you make the parts in your store? they look nice. most people here know about them, i think most folks who opt not to use them are penny pinching.

Dave,
Yes, my bearing blocks include the cost of a 1/2" bearing. They're only about $2 from VXB if you buy 10 at a time, but I added them to the assembly to save people an extra order and shipping charge.

Best regards,

Ahren
www.cncrouterparts.com

[ahren]

Dave,

Thanks for the compliments. I make prototypes and small production runs on my equipment, but volume parts are made by my supplier, who uses top notch CNC equipment (Fadal 4020 machines). Most parts are tumble deburred after machining to give them a nice finish. All of my parts are made in the US, aside from the fasteners and bearings.

There's certainly nothing wrong with penny pinching -- my business depends on it! While I certainly enjoy selling parts, I also try to make sure people get the best possible solution for their machines and situation, which is why I like participating in these forums. After building two machines of my own, I have been through a lot of the pain that comes with doing things a little too cheaply .

Good luck with your build, and feel free to contact me if there's anything I can help with!

Best regards,

Ahren
www.cncrouterparts.com

[GreenvilleDave]

No problem. I guess even though it may not work out, i'm going to go with an all-thread based design and skate bearings for now. that keeps costs very low, and should let me get going more quickly.

An all-thread based design will probably work well enough to 'bootstrap' a better machine, and i'm sure there are lots of lessons i'll learn that ill want to do over on the next one anyway. No sense trying to build the 'perfect' machine my first try -- i know better than that

thanks for the help!

Dave,

Thanks for the compliments. I make prototypes and small production runs on my equipment, but volume parts are made by my supplier, who uses top notch CNC equipment (Fadal 4020 machines). Most parts are tumble deburred after machining to give them a nice finish. All of my parts are made in the US, aside from the fasteners and bearings.

There's certainly nothing wrong with penny pinching -- my business depends on it! While I certainly enjoy selling parts, I also try to make sure people get the best possible solution for their machines and situation, which is why I like participating in these forums. After building two machines of my own, I have been through a lot of the pain that comes with doing things a little too cheaply .

Good luck with your build, and feel free to contact me if there's anything I can help with!

Best regards,

Ahren
www.cncrouterparts.com