[deejayspinz]

Hey all,

Another noob question. I am upgrading my existing MyDIYCNC and made the Y axis longer. As a result of widening the unit, I am also upgrading the linear rods to 5/8" (from 3/8"). I also got a set of linear bearings from ebay (sample below) to mount to the Z axis. I did a check by sliding the bearing onto the rod and noticed that there is some play. I am able to rattle the bearing block and I figure there is about 1mm play on either side as I do this by hand. I tried putting some grease in there to see if that would tighten things up, but the play is still there. Is this normal? Is there a way to adjust these units?

I expect that if I were to put this all together, there would be much more play at the tip of the mill. I can see the weight of the Z axis helping a bit as it's weight will hold the unit down, but if my cut speeds and material density are greater than this force, it will cause movement.

Is there a way to remove some of this play? e.g. mount the bearings so they are not exactly parallel with the rods (using very thin washers at one side maybe)? Did I get crappy parts?

[bikedude987]

If there is actually as much play as you said, you either have the wrong bearings or the wrong shaft. There should be little (if cheap) to no (if good) play in the set.

What direction is the play in?

[deejayspinz]

Maybe 1mm may be exaggerating it.. but there is play. When I slide the bearing on by hand and take the bearing and rock it back and forth, the play is there.

Here's a link to the bearings I ordered. However, they sent me the wrong ones (correct diameter but shorter units). They are 16mm ID bearings. My rods are 5/8". If both of these are precision units, then I guess the difference may be that the bearings truly have an ID of 16mm but the rods (translated to metric) are actually 15.875mm... Maybe I should have gone the matched route and ensured that the rods/bearings came with one order and ensure they are matched. I researched some of the open bearing pillow blocks and have seen some that have adjustment screws to put tension on the inner bearing inside the block. In my case, I'd have to get an open bearing and mod the block to do this... I'm waiting for the seller to send me the correct (longer bearings). Hopefully they will have a tighter tolerance.

[bikedude987]

"then I guess the difference may be that the bearings truly have an ID of 16mm but the rods (translated to metric) are actually 15.875mm..."

Seems to me you know what the problem is...Why are you surprised there is slop when you ordered undersized rods to begin with?:violin:

[LongRat]

Yes that is a mile out. You know what the problem is. Those bearings should have NO play in them and what you have will be completely useless for your machine. Get them changed for units the right size.

[deejayspinz]

Yes that is a mile out. You know what the problem is. Those bearings should have NO play in them and what you have will be completely useless for your machine. Get them changed for units the right size.

Thx. I'm going to order an adjustable set of bearings and replace the ones that are in there, then tap the block for some adjustment screws. That should fix it.

[whateg01]

Why not just order the right size bearing? Or new rod to match the bearings you have, which might be the less expensive way to go?

[deejayspinz]

Why not just order the right size bearing? Or new rod to match the bearings you have, which might be the less expensive way to go?

Agreed that this makes sense, but having a limited budget and being in Canada limits the choices. Ebaying 5/8" linear bearings/blocks are $25 a piece. Figure I'd need 4 of these for the Y axis. Given that I goofed by getting imperial rods and metric bearings, I'm trying to figure out the most economical way to make it right.

[hndswthtshdws]

Any fastener supply should be able to get you precision rods in the correct diameter. These usually come in 3' or 1m lengths. Prices are surprisingly low. For my rep rap it was cheaper to buy local than ebay.

[LongRat]

How exactly do these adjustable blocks work? I can't see how they could for a recirculating ball type bearing. You are certainly better off replacing the rods for some of the correct diameter.

[deejayspinz]

How exactly do these adjustable blocks work? I can't see how they could for a recirculating ball type bearing. You are certainly better off replacing the rods for some of the correct diameter.

Here: See this bearing block .

[whateg01]

You say you are trying to cut cost, but then link a $75 (w/shipping) item that you would need 4 of? That doesn't make sense. You could probably get the 0.005" you apparently need, but why go the expensive route?

[deejayspinz]

You say you are trying to cut cost, but then link a $75 (w/shipping) item that you would need 4 of? That doesn't make sense. You could probably get the 0.005" you apparently need, but why go the expensive route?

Umm.. don't recall saying I was buying these... I was showing them as an example to answer the question about what adjustable bearings are.

[whateg01]

Oh, sorry. I thought you said...

...I'm going to order an adjustable set of bearings... That should fix it.

My bad.

[deejayspinz]

Oh, sorry. I thought you said... My bad.

As I said before, I was providing a link as a SAMPLE to answer LongRat's question. Do you see any statement in that response that says "here's what I am going to buy" ? Jeeze... I purposely started this thread indicating I was a noob. I 'get' that I have things to learn with respect to CNC. I'm not looking to get attacked because of someone's poor interpretation of what they are reading. Go threadcrap somewhere else. You are wasting my and other's time who are trying to help here..

[mactec54]

deejayspinz

The ajustable bearing blocks are ok, but you still have to buy the right ones for the size shaft you are going to use, if your shaft is .625 ( 5/8) then the ajustable bearing block has to be for .625 ( 5/8 ) Rods

You can not get a Bearing Block for 16mm Bearings & ajust it to the .625 ( 5/8 ) Shaft

[deejayspinz]

deejayspinz

The ajustable bearing blocks are ok, but you still have to buy the right ones for the size shaft you are going to use, if your shaft is .625 ( 5/8) then the ajustable bearing block has to be for .625 ( 5/8 ) Rods

You can not get a Bearing Block for 16mm Bearings & ajust it to the .625 ( 5/8 ) Shaft

Thx for the tip. Just trying to decide if I buy new bearing blocks (as I already have the 5/8 rods) or get new rods (since I also have 16mm bearing blocks).. Limited retailers in Canada and higher prices makes for a bit of a challenge. E.g. - I paid $55 for 2x 5/8" x 26" precision drill rods at Fastenal. I'm ok with that even though these are less in the US, but shipping kills it for me. It's a toss-up between getting 2x 16mm rods to make it right, or chance ebay'in Chinese 5/8" bearing blocks (which are hard to find at a reasonable cost). Lots of 16mm bearing blocks though.. Just going to keep searching to see what the better approach is.

Edit: Just talked to the guys @ Fastenal (great guys BTW), and they can get me 16mm drill rod. So, I'll just exchange the 5/8" rods I bought for these and give that a go. $70+tax for 2 is bearable..

[mactec54]

deejayspinz

You can not use the precision drill rods, with the linear Bearings, You have to use the hardened rods that go with the linear Bearings, The drill rod is to soft for the Bearings to run on, The Drill rod is ok for plain bushings, Like brass/Plastic Etc

[bikedude987]

No where in the link did I see the word 'adjustable'. I believe the slit on the side is there becaust that is a split clamp to secure the bearing to the block. a linear bearing looks like this

http://www.isotechinc.com/images/slide-bushing-big.jpg

without the block. The block is just a cylindrical-to-planar adapter.

BTW, I'm an engineer and I've never even heard of an adjustable diameter bearing. of any type...

As others have said the correct diameter precision ground shafting should not be expensive. Mcmaster, Misumi, ebay, THK, Thompsone (who sells to mcmaster), etc...

[deejayspinz]

No where in the link did I see the word 'adjustable'. I believe the slit on the side is there becaust that is a split clamp to secure the bearing to the block. a linear bearing looks like this

http://www.isotechinc.com/images/slide-bushing-big.jpg

without the block. The block is just a cylindrical-to-planar adapter.

BTW, I'm an engineer and I've never even heard of an adjustable diameter bearing. of any type...

As others have said the correct diameter precision ground shafting should not be expensive. Mcmaster, Misumi, ebay, THK, Thompsone (who sells to mcmaster), etc...

I'm not an engineer, but like to pretend that I am, and found them pretty quickly ;-) Here you go.. Adjustable linear bearing. They are all over Ebay, so I'm pretty sure they exist. :-)