Advice needed on sanding small items for production

[HowdyMurph]

Hello, I'm trying to figure out best sanding solution for this job and would love any advice please...

I'm using a CNC to cut batches of small Poplar plywood flowers and then doming / finishing the backs of each on a lathe.

I'm looking for a way to then get a smoother finish around the sides of each whilst protecting the painted front face. The challenge is the various flower shapes make the contoured edge tricky to sand for a production situation. I've attached an example pic but there are lots of different shapes all around 25mm thick

Currently I'm using an abrasive scruff ball on my lathe. I'm holding pairs of flowers with the painted front faces together to prevent chipping. Whilst the method does work it can leave coloured residue from the scruff ball on the wood and also wears the scruff ball down really quickly. I need to be able to produce 100+ items a day so looking for a more viable way of doing this?

I then finish with wax buffed with a domed polishing brush on the lathe which works well as the long fibres get into all the contours.

Is there something you could recommend that would be better than the scruff ball to smooth / eliminate furries on the plywood edges? I'm wondering about trying a harder bristled brass/steel brush or similar in the lathe but maybe this would be too aggressive? All ideas or advice most appreciated!

 

[Ollie78]

Just wondering if you could optimize the toolpath so you need to do less sanding, in the long run this would be the most efficient way to reduce the problem.

Are you removing tabs from the cnc routing process ? if so maybe try vacuum workholding or the masking tape and super glue strategy so you don`t need tabs.
look into a power file these are incredibly efficient at material removal, perhaps a belt system like knifemakers use, maybe a bench grinder with an abrasive wheel similar to your scuff pad method only much quicker.

Ollie

 

[peter-harrison]

A small vertical belt sander? They seem to go for £150-500 or so.
Or a power file held in a jig? £50 or so.

 

[HowdyMurph]

Just wondering if you could optimize the toolpath so you need to do less sanding, in the long run this would be the most efficient way to reduce the problem.

Are you removing tabs from the cnc routing process ? if so maybe try vacuum workholding or the masking tape and super glue strategy so you don`t need tabs.
look into a power file these are incredibly efficient at material removal, perhaps a belt system like knifemakers use, maybe a bench grinder with an abrasive wheel similar to your scuff pad method only much quicker.

Ollie

Thanks Ollie, I'll look into all those more. I have a bench grinder for sharpening lathe tools so maybe would be able to get a suitable wheel for that? Nylon bristle type of thing? Keen to find something i can hold the work up against rather than gripping it for this step for speed and to avoid marking the work. The skinny sanding belts also look interesting - I guess that would take more effort on my part to hold the work accurately against it than a wheel though ha.

On the CNC my toolpaths are as optimised as i can get it i think! The alternating direction of the grain on the ply is making it tricky to get a super clean finish. I am using tabs but because they are only a few mm deep they're removed by the doming step on the lathe so that works pretty well. Would love a vacuum machine bed eventually!

 

[HowdyMurph]

A small vertical belt sander? They seem to go for £150-500 or so.
Or a power file held in a jig? £50 or so.

Thanks! Yes i like the look of the skinny belt sanders but have never tried one. I'm just thinking i will have to carefully follow the wood contour if using one of them so would need more concentration. Wondering if there's a more forgiving wheel / brush kind of thing that the work can be pushed into and rotated with less precision?

 

[Ollie78]

Thanks Ollie, I'll look into all those more. I have a bench grinder for sharpening lathe tools so maybe would be able to get a suitable wheel for that? Nylon bristle type of thing? Keen to find something i can hold the work up against rather than gripping it for this step for speed and to avoid marking the work. The skinny sanding belts also look interesting - I guess that would take more effort on my part to hold the work accurately against it than a wheel though ha.

On the CNC my toolpaths are as optimised as i can get it i think! The alternating direction of the grain on the ply is making it tricky to get a super clean finish. I am using tabs but because they are only a few mm deep they're removed by the doming step on the lathe so that works pretty well. Would love a vacuum machine bed eventually!

Sounds like a suitable wheel on the bench grinder is the way forward for the sanding. Maybe some of these type of thing Flange flap wheels.
I suggest making a sanding holder using the cnc machine, just a negative of the shape you produce, add some way of clamping or gripping it. This will give you safe repeatable holding for speed and keep fingers away from the abrasive.

Are you using a compression bit? these are superb for plywood I can get a totally smooth cut on birch ply with a 6mm compression bit.

Ollie

 

[HowdyMurph]

Sounds like a suitable wheel on the bench grinder is the way forward for the sanding. Maybe some of these type of thing Flange flap wheels.
I suggest making a sanding holder using the cnc machine, just a negative of the shape you produce, add some way of clamping or gripping it. This will give you safe repeatable holding for speed and keep fingers away from the abrasive.

Are you using a compression bit? these are superb for plywood I can get a totally smooth cut on birch ply with a 6mm compression bit.

Ollie

Thanks Ollie yes they look interesting! The sanding holder is a great shout - I'll definitely experiment with that, may be able to hold a stack of the smaller pieces to speed things up.

I'd love to get the cut super clean on the CNC - it's all relatively new to me it's a kit build machine i got 18 months ago so it's been a pretty steep learning curve! I'm using a compression bit on the 6mm poplar for smallest pieces as i need a v clean front and back face - I do still get slight tear out / fuzzies on the sides in places but have tried so many test cuts at different speeds and feeds not sure what else would improve it... think it may be best i can do with Poplar ply being a bit softer than birch?

The 25mm thick poplar it doesn't matter what the back face looks like as its getting lathed so I'm currently using cheap straight end mills as i get a nice clean front face and pretty decent cut throughout. I've tried treating the poplar with a penetrating sealer before v-carving to firm up the fibres but didn't see any improvement. The things that seem to make the most difference are 1) low moisture content - if i use a board that's been in the garage a while it definitely cuts worse! 2) clear varnish on the top surface before cutting gives me a cleaner top edge 3) super sharp new bit. Open to all suggestions if there's anything else i should be doing!

Thanks, Nat!

 

[Ollie78]

Thanks Ollie yes they look interesting! The sanding holder is a great shout - I'll definitely experiment with that, may be able to hold a stack of the smaller pieces to speed things up.

I'd love to get the cut super clean on the CNC - it's all relatively new to me it's a kit build machine i got 18 months ago so it's been a pretty steep learning curve! I'm using a compression bit on the 6mm poplar for smallest pieces as i need a v clean front and back face - I do still get slight tear out / fuzzies on the sides in places but have tried so many test cuts at different speeds and feeds not sure what else would improve it... think it may be best i can do with Poplar ply being a bit softer than birch?

The 25mm thick poplar it doesn't matter what the back face looks like as its getting lathed so I'm currently using cheap straight end mills as i get a nice clean front face and pretty decent cut throughout. I've tried treating the poplar with a penetrating sealer before v-carving to firm up the fibres but didn't see any improvement. The things that seem to make the most difference are 1) low moisture content - if i use a board that's been in the garage a while it definitely cuts worse! 2) clear varnish on the top surface before cutting gives me a cleaner top edge 3) super sharp new bit. Open to all suggestions if there's anything else i should be doing!

Thanks, Nat!

Well, all machines are different but from memory I think I am cutting at 3metres a minute with 20,000 rpms using a 6mm 2 flute compression bit does this seem anywhere near what you are working with?

What you could try is leaving a slight amount of material and do a finish pass of 0.5 to 1mm to clean it up. It takes a bit longer but may help.
Also are you climb cutting or conventional, this can make a difference.

I know there are calculators for working out the cuts per mm for a given spindle and feed speed and cutter which is in the end what matters, if your spindle is not fast enough for a 2 flute you could try a 3 flute cutter for example. More cuts per spin so less speed needed.
Each cutter should have a recommended speed for the correct "chip load" which can be found on the manufacturers website.

Ollie

 

[Simon89]

Would the additional cost of birch ply be negated by the time saved sanding, assuming you get a cleaner cut?

 

[Sachakins]

Does it have to be ply, maybe try solid wood.

Bit choice makes a big difference, I've switched to Spe Tools solid carbide bits, it's improved cuts greatly, only thing is they're expensive.
Also put a finishing cut in your tool paths, say 0.5 to 1mm.
Other option is do a final profile cut with a 60° v bit to chamfer a tiny edge to remove the fuzzies

 

[HowdyMurph]

Would the additional cost of birch ply be negated by the time saved sanding, assuming you get a cleaner cut?

Sorry for the very delayed reply, this was a good shout thanks for your suggestion... I've bought in some birch ply to compare and i can get this to v-carve and cut cleanly on the machine with zero sanding. So much faster. Aesthetically though i much prefer the pale uniform look of the poplar, the dark lines between layers on the birch don't look great. So now I'm trying to figure out whether i can find something that machines as well as the birch but looks more like poplar!?

 

[Jacob]

Sorry for the very delayed reply, this was a good shout thanks for your suggestion... I've bought in some birch ply to compare and i can get this to v-carve and cut cleanly on the machine with zero sanding. So much faster. Aesthetically though i much prefer the pale uniform look of the poplar, the dark lines between layers on the birch don't look great. So now I'm trying to figure out whether i can find something that machines as well as the birch but looks more like poplar!?

Would like to see what people do with CNC. Photos could be interesting?

 

[HowdyMurph]

A finished bouquet...

 

[HowdyMurph]

Comparison of Poplar V Birch, front & back...

 

[HowdyMurph]

Does it have to be ply, maybe try solid wood.

Bit choice makes a big difference, I've switched to Spe Tools solid carbide bits, it's improved cuts greatly, only thing is they're expensive.
Also put a finishing cut in your tool paths, say 0.5 to 1mm.
Other option is do a final profile cut with a 60° v bit to chamfer a tiny edge to remove the fuzzies

Thanks for this & sorry I've not replied sooner

I'm going to test out some solid beech / maple but I'm quite attached to the look of the poplar ply for it's paleness & when i lathe the back i like how you get all the visible rings. There's pics above on the thread to show this as i know it's hard to imagine what I mean!

I use a good quality Amana 90 degree V bit for the V carve but even with that i'm having to spray cellulose sanding sealer followed by a full depth finishing pass to get a clean enough cut. Poplar seems to be a nightmare for leaving fluffy bits in places where the bit is going with the grain.

Currently for the profile cut on the CNC i use a 6mm carbide tipped 2 flute straight end mill and set it to do a reverse direction last pass a fraction of a mm closer. Is that what you mean by finishing path or would you run a separate pass with a different bit? I'm going to order a couple of high quality solid carbide bits to compare the finish.

 

[HowdyMurph]

Well, all machines are different but from memory I think I am cutting at 3metres a minute with 20,000 rpms using a 6mm 2 flute compression bit does this seem anywhere near what you are working with?

What you could try is leaving a slight amount of material and do a finish pass of 0.5 to 1mm to clean it up. It takes a bit longer but may help.
Also are you climb cutting or conventional, this can make a difference.

I know there are calculators for working out the cuts per mm for a given spindle and feed speed and cutter which is in the end what matters, if your spindle is not fast enough for a 2 flute you could try a 3 flute cutter for example. More cuts per spin so less speed needed.
Each cutter should have a recommended speed for the correct "chip load" which can be found on the manufacturers website.

Ollie

Thanks Ollie & sorry for the super delayed reply.

Yes similarly mine is cutting at around 2.5metres a minute feed rate with spindle speed 18k rpm. I've been using 6mm straight bit as I don't need the bottom face to cut cleanly and I'm a bit nervous of using a compression bit on this thick 25mm poplar - do you find the compression bit gives you a cleaner cut all the way through compared to straight / downcut bits or is the main improvement the clean front & back faces?

I'm using climb cutting as found that got the cleanest results but i can see that the areas that fuzzies are left seem to be where the router is travelling in the same direction as the grain on Poplar.

Since I made this thread I've tried using birch ply and can get that really clean cut with no finishing which is brilliant but i prefer aesthetically the poplar so I'm still keen to figure it out. I'm going to order a couple of high quality 6mm bits to test on the poplar to see if i can get a cleaner finish - do you have any favourite bits you'd recommend?

Thanks, Natalie

 

[Sachakins]

Thanks for this & sorry I've not replied sooner

I'm going to test out some solid beech / maple but I'm quite attached to the look of the poplar ply for it's paleness & when i lathe the back i like how you get all the visible rings. There's pics above on the thread to show this as i know it's hard to imagine what I mean!

I use a good quality Amana 90 degree V bit for the V carve but even with that i'm having to spray cellulose sanding sealer followed by a full depth finishing pass to get a clean enough cut. Poplar seems to be a nightmare for leaving fluffy bits in places where the bit is going with the grain.

Currently for the profile cut on the CNC i use a 6mm carbide tipped 2 flute straight end mill and set it to do a reverse direction last pass a fraction of a mm closer. Is that what you mean by finishing path or would you run a separate pass with a different bit? I'm going to order a couple of high quality solid carbide bits to compare the finish.

I'd do a separate finish pass with a different bit, a downcut bit.

 

[worn thumbs]

Would like to see what people do with CNC. Photos could be interesting?

A couple of pieces to satisfy Jacob's curiosity.One is a simple piece of V-carving and the other is a template for a model part.I will admit that using 1.25mm cutters is a bit stressful.

 

[J-G]

I will admit that using 1.25mm cutters is a bit stressful.

Most of my CNC work uses 1mm though much is 0.6mm - but I will admit that is usually only as a very final pass taking off <0.2mm -

and expletives are not infrequent!!

 

[Jacob]

What would be the major product of CNC and wood? Is it used on an industrial scale at all?