Thread: Bitser

Originally Posted by chrisb691

I know it is a bit odd to build/design at the same time, but my existing machine is not terribly accurate and I'm figuring stuff out as I get actual sizes from the build.

I think you may find that almost all of us do things this way. Just start building and make it up as you go along.

Originally Posted by chrisb691

Z is using 12mm supported rails/bearings, and a 12mm ballscrew. I'm aiming for 150mm travel on z, but, as can be seen from the pics, I cocked up when ordering the ballscrew and will need to order a longer one.

I'm not sure what the worry is on the Z axis. You seem to have a screw that is of adequate length. You may just need to offset the mounting of the router so that it is below the actual screw.

I realise that this is not as pretty as having a longer screw, but it is a lot cheaper (because you already have it) and does the same job.

Originally Posted by Bob Willson

I'm not sure what the worry is on the Z axis. You seem to have a screw that is of adequate length. You may just need to offset the mounting of the router so that it is below the actual screw.

I realise that this is not as pretty as having a longer screw, but it is a lot cheaper (because you already have it) and does the same job.

Thanks Bob,

You are correct, I can get the full 150mm travel. The nut will just be on the ballscrew at bottom of travel. I'm not at all ure that I will ever need 150mm, so I might cut it back to 140mm for safety's sake.

Originally Posted by chrisb691

Thanks Bob,

You are correct, I can get the full 150mm travel. The nut will just be on the ballscrew at bottom of travel. I'm not at all ure that I will ever need 150mm, so I might cut it back to 140mm for safety's sake.

Cut, I think you mean grind the hell out of it. Ball screws are tough!

I actually meant reduce the travel via design.

Making progress, albeit somewhat slowly.

Pic 1 is the tortion box bed in glue up.

Pic 2 the bed complete and skinned.

Pic 3 The Z-axis taking shape. Forgot to order the bearings for this, and am now waiting delivery so I can fit the ball screw nut. But it looks like it will go together okay.

Just confirming some sizes, and then I can order the balance of the rails/bearings/ball screws etc. Almost finished drawing up the gantry sides, and should be cutting them soon.

Looks interesting Wondering if there is a bearing support on the other end of the ballscrew on the z axis

Originally Posted by Bupton

Looks interesting Wondering if there is a bearing support on the other end of the ballscrew on the z axis

No bearing the bottom. It's only short, and wont need to rotate very fast, so I'm just letting it float.

Making steady progress now, tha last of the major conponents have been cut. Only the small stuff to go now, such as the motor mounts.

Pic 1. The gantry sides have been cut, but still need the edges cleaned up. These are only dowelled together at this time. Eventually they will be glued, and screwed. All the holes lined up well, so I'm hopefull everything will go together plumb.

Pic 2. The gantry bearing supports. These will hold 3 bearings on each side of the gantry. At nearly 200mm separation on the bearings, I'm hoping that there will be no racking of the gantry. Height positioning is via dowels, but if things don't work out as intended, I have have allowed for adjusting bolts. Once it's all true, I'd drill in a couple of new dowels.

Pic 3. The gantry lower tortion box, and nut holder.

I've ordered the balance of my parts from Chai, but have probaby got another week or so before they get here. In the meantime, I'll do a dry fit of everything I have made, just to get a rough sense of how position has worked out. Then pull it down, refine all the edges etc, and prep it all for painting. I could actually live happily with it all unpainted, but want to prevent moisture issues with the mdf.

I still have the motor mounts to work out, but will wait until I get the rest of the parts so that I have something to work with.

Got the rest of the parts from Chai yesterday. Opened the parcel, with a great deal of excitement. Once I got everything out, the first problem became apparent, in that the ballscrews wouldn't fit into the end supports. I spent a few hours hand polishing the machined ends, until I got the end supports fitting. In the scheme of things, the time taken was not much, compared to the total build time, but it was annoying.

I had ordered a 300mm 12mm ballscrew, to replace the 250mm one I got earlier. This was to enable me to get full movement, without risking the ballscrew nut coming off the end of the thread. The last one fitted a BK10 end support, also supplied by Chai. Being naive, I just ordered the longer one that I needed. This one had been machined differently, and was too small to fit the BK10. I figured that I would need a BK8, but couldn't find such a beast listed anywhere. I emailed Chai, and got the response that it had been machined to standard. My reply was that since I had received 2 12mm ballscrew with differing machining, his 'Standards' seemed to be a bit flexible, and would he give me a price for a BK8 to suit the new one.

Chai replied that he didn't have BK8s, and what would I like to do now. I requested a price for a replacement ballscrew, machined to suit a BK10, and would he please ensure that it would fit. He came back with an offer to supply the replacement free, if I would pay the $18 freight. I have accepted this...at least he is trying.

This morning I have done a test assembly, and, apart from an issue with the gantry trucks, everything lines up properly, with all the positioning dowels going in. I have cocked up the bearing positioning, on the trucks, by 5mm per side, and will need to make new ones. But this is a minor issue, and I am well pleased with the overall result.

I have 600mm x 490mm travel, so the cutting area will be a little less than that. With a 3mm bit fitted, I have 170 over the bed. Allowing for the table, and spoil board, this will give me at least 130mm capacity on Z.

Now that I have got it assembled I will look at what is needed for the motor mounts, then take it apart, so that I can make the balance of parts needed. I bought drag chains with the rest of the parts, but have no idea, at this stage, how to fit them. But that can't be too difficult....I hope.

Originally Posted by chrisb691

the ballscrews wouldn't fit into the end supports

They are made with an interference fit of a few thousandths of a mm. If you had frozen the end of the shaft they would probably have slipped straight on.

Originally Posted by chrisb691

I have 170 over the bed. Allowing for the table, and spoil board, this will give me at least 130mm capacity on Z.

If you have 170mm over the bed then you should be able to get 169.9 mm capacity. You just need to have the router mounted a little higher in the carrier, or the carrier mounted a little higher on the Z axis

Originally Posted by Bob Willson

They are made with an interference fit of a few thousandths of a mm. If you had frozen the end of the shaft they would probably have slipped straight on.

I don't think I could have got the machine in the freezer, besides which, the interference was more than 0.1mm.

Originally Posted by Bob Willson

If you have 170mm over the bed then you should be able to get 169.9 mm capacity. You just need to have the router mounted a little higher in the carrier, or the carrier mounted a little higher on the Z axis

The bed is not the machining surface. When I construct the T-slot table, this will reduce the distance by 19mm. Add a 16mm spoilboard, and I would get 135mm. This would seem to more than adequate for anything I would wish to do.

Originally Posted by chrisb691

I don't think I could have got the machine in the freezer,

I didn't actually expect you to put the thing into the fridge. Just a bag of ice would have done it.

Originally Posted by chrisb691

besides which, the interference was more than 0.1mm.

OK, that is a lot to be out.

Originally Posted by chrisb691

The bed is not the machining surface. When I construct the T-slot table, this will reduce the distance by 19mm. Add a 16mm spoilboard, and I would get 135mm. This would seem to more than adequate for anything I would wish to do

It all sounds good then.

Hi Chris,
If he sends you a ballscrew without a nut then get back here to get some advice on how to transfer the nut.
Machine is looking sturdy.