Drill compensation for full dentures.

[nvarras]

I'm just trying to wrap my head around this. Is there anything out there that I can read about the subject? My mill uses a 1.0mm bur for the intaglio. 3shape came set at .8. What is the reasoning for this and is there a more accurate setting that i can use. I am new to milling if you couldn't tell...

 

[user name]

3Shape was assuming you were going to use a .6 bur perhaps?
On crowns using a 1.0 mm bur for the intaglio, Im set at 1.2.

@brayks ??

 

[2thm8kr]

I find 1.1-1.2 works great in exocad settings(1mm roughing). However, that is stacked on top of all the other setting for the design...

 

[zero_zero]

You might want to look into your cutting strategies and tooling instead...just sayin'

 

[CoolHandLuke]

drill compensation for anything should be set at 110%-120% of the Bur RADIUS; so in a diameter 1.0mm finishing tool, drill compensation should be between 0.55 and 0.6mm. on a denture however this still leaves a lot of high spots and rough edges, and you can tell it leaves these by running a cotton ball around the rim of the denture once its out of the mill. there will be catches. due to spiral patterns and uneven surfaces, the surface quality will also have left many topical lines. you will not get those smoothed off with the finishing pass, it will take a specially devised second finishing pass to remove those lines. the majority of CAM don't really do that and i'd recommend it only on a 2mm intaglio finishing pass.

i'd bet that 3shape setting of 0.8mm was thinking the final finishing would be done with a 2mm tool.

 

[sidesh0wb0b]

drill compensation for anything should be set at 110%-120% of the Bur RADIUS; so in a diameter 1.0mm finishing tool, drill compensation should be between 0.55 and 0.6mm. on a denture however this still leaves a lot of high spots and rough edges, and you can tell it leaves these by running a cotton ball around the rim of the denture once its out of the mill. there will be catches. due to spiral patterns and uneven surfaces, the surface quality will also have left many topical lines. you will not get those smoothed off with the finishing pass, it will take a specially devised second finishing pass to remove those lines. the majority of CAM don't really do that and i'd recommend it only on a 2mm intaglio finishing pass.

i'd bet that 3shape setting of 0.8mm was thinking the final finishing would be done with a 2mm tool.

would love to know more from you on this. if i run drill comp at 110%-120% of radius for milling wax, the patterns dont fit at all. for example: .6mm finish tool intaglio but i get the best internal fits at 1.04 drill comp
with your math you think id get better fits at .63-.66 drill comp? i can run a test mill and post results if youd like

 

[CoolHandLuke]

if the 0.6 mm tool is just doing spot finishing, then you are really finishing with 1mm, so 1.04 makes sense.

if you want to use 0.6mm for finishing you'll have to create a toolpath to make it do spiral full surface cutting - but that would break the tool 100% of the time.

this is the disconnect people have about drill compensation and finishing. spot finishing doesn't count. it doesn't cut the whole surface.

 

[nvarras]

You might want to look into your cutting strategies and tooling instead...just sayin'

I guess what you are saying is that it doesn't matter what compensation 3shape uses if I am putting it through millbox before it hits the mill because the compensation will be changed in there? So I need to look at millbox rather than 3shape.

 

[JMN]

I guess what you are saying is that it doesn't matter what compensation 3shape uses if I am putting it through millbox before it hits the mill because the compensation will be changed in there? So I need to look at millbox rather than 3shape.

Cutting strategies is important as @CoolHandLuke was pointing out that the smallest burr will *not* be finishing on everything so if you are fiddling your data with the expectation that the .6mm will be doing a fine pass on the whole, you need to create or verify the CAM path that is doing the work you expect.

Does that help?

 

[CoolHandLuke]

I guess what you are saying is that it doesn't matter what compensation 3shape uses if I am putting it through millbox before it hits the mill because the compensation will be changed in there? So I need to look at millbox rather than 3shape.

it does matter.

if you set compensation too small then the millbox software will not be able to reach those narrow pockets, and leave material behind. if you set compensation too large you may run into thickness issues, bite issues, or load bearing issues where you create a weak spot in your object.

millbox won't "overwrite" or modify your compensation, if anything it will error on the side of leaving material behind in an effort to save the object from not disintegrating in the mill or burning a tool.

you have to harmonize 3shape and millbox.

 

[sidesh0wb0b]

if the 0.6 mm tool is just doing spot finishing, then you are really finishing with 1mm, so 1.04 makes sense.

if you want to use 0.6mm for finishing you'll have to create a toolpath to make it do spiral full surface cutting - but that would break the tool 100% of the time.

this is the disconnect people have about drill compensation and finishing. spot finishing doesn't count. it doesn't cut the whole surface.

interesting, i will have to take a look and see. the only issue i ever have is with milling wax, and maybe this has been my stumbling block. i appreciate you shedding light on it if thats the case!
*edit* being that 1.04 is just shy of the 1.05-1.1 range (110%-120% as you mentioned),would you expect another bump into that range would positively affect internal fit of wax patterns? generally speaking they come out far too loose.

 

[CoolHandLuke]

if they are coming out loose, double check the tools and the machine. you may be seeing a runout issue.

how to check this digitally would be to mill a large span bridge 5-9 units or other large item with that same wax strategy and tools, and use GOM to compare the milled vs the design and see the distribution of differences.

 

[sidesh0wb0b]

if they are coming out loose, double check the tools and the machine. you may be seeing a runout issue.

how to check this digitally would be to mill a large span bridge 5-9 units or other large item with that same wax strategy and tools, and use GOM to compare the milled vs the design and see the distribution of differences.

this might be silly, but since its milling wax with the same tools as the zirconia....wouldnt i see a similar issue with fit on the zirc? which i do not.

 

[CoolHandLuke]

it may be the same tools but is it the same toolpaths, speeds,? i doubt it. in fact when you say its the same tools, if theres a fit discrepancy i'll guarantee its a toolpath issue.

 

[sidesh0wb0b]

it may be the same tools but is it the same toolpaths, speeds,? i doubt it. in fact when you say its the same tools, if theres a fit discrepancy i'll guarantee its a toolpath issue.

oddly enough, i had the same issues across design softwares too. 3shape/exocad doesnt matter.
however, ive been able to get it better, much much better. though i still want it as close to perfect as possible