Collet vs holder run out

[Batmanacw]

I was considering buying some endmill holders to install some of my more used endmills and a couple holders for an edge finder and tap guide.

I only have a few end mill holders. I checked a 3/4" Shars endmill holder I turned down for my annular cutter and it had exactly 0.001" of run out.

I really only want 1/4, 3/8, and 1/2. I end up doing more hogging with smaller endmills than larger anyway.

I checked a 3/8" R8 collet with a carbide endmill and I had 0.0004". I knew the collet would be more accurate but how accurate do I really need?


Assuming a decent quality, what is the practical accuracy limitation on an R8 endmill holder?

 

[RJSakowski]

An edge finder doesn't need a low runout holder as it is self centering by nature. That is it's strong point, A tap guide also doesn't need a low runout holder as the tap wrench usually has enough play that any runout will eclipse the wobble.

It is my understanding that the primary objective for low milling tool runout is longer tool life. There is the consideration of nominal versus effective tool diameter but for a tool with .001" TIR, this only amounts to a half thousandth. For critical dimensions, I would make a test cut and measure anyway. For CNC work, I would enter the effective tool diameter into my tool table and use that diameter for determining the tool paths.

 

[Batmanacw]

An edge finder doesn't need a low runout holder as it is self centering by nature. That is it's strong point, A tap guide also doesn't need a low runout holder as the tap wrench usually has enough play that any runout will eclipse the wobble.

It is my understanding that the primary objective for low milling tool runout is longer tool life. There is the consideration of nominal versus effective tool diameter but for a tool with .001" TIR, this only amounts to a half thousandth. For critical dimensions, I would make a test cut and measure anyway. For CNC work, I would enter the effective tool diameter into my tool table and use that diameter for determining the tool paths.

I'm all manual. I'm just considering how bad 0.001" for tool life. Can I trust any end mill holders to do significantly better?

 

[RJSakowski]

I'm all manual. I'm just considering how bad 0.001" for tool life. Can I trust any end mill holders to do significantly better?

I have that much runout and more on my Tormach.

Actually, it is my understanding that end mill holders have better runout than collets. For really low runout, tools are shrink fit into holders and both are discarded when the tool reaches end of life.

I happen to use collets on the Tormach because of the TTS system although I have a few R8 end mill holders as well. The TTS system uses a 3/4" R8 collet to draw the TTS tool holder into positive registration with the spindle face. The convenience of not having to re-reference tools with every tool change led me to adopt this system for my RF30 clone as well.

 

[ChazzC]

I have set of SHARS 3/8", 1/2"& 5/8" end mill holders that I got when I bought my Mini-Mill. I still use them if I need the extra reach, but since Mini-Mills are Z-challenged I mostly use R-8 Collets (need to use R-8 Collets with Metric end mills anyway).

 

[Batmanacw]

I have set of SHARS 3/8", 1/2"& 5/8" end mill holders that I got when I bought my Mini-Mill. I still use them if I need the extra reach, but since Mini-Mills are Z-challenged I mostly use R-8 Collets (need to use R-8 Collets with Metric end mills anyway).

How much do your tools run out in your end mill holders.

 

[Batmanacw]

I have that much runout and more on my Tormach.

Actually, it is my understanding that end mill holders have better runout than collets. For really low runout, tools are shrink fit into holders and both are discarded when the tool reaches end of life.

I happen to use collets on the Tormach because of the TTS system although I have a few R8 end mill holders as well. The TTS system uses a 3/4" R8 collet to draw the TTS tool holder into positive registration with the spindle face. The convenience of not having to re-reference tools with every tool change led me to adopt this system for my RF30 clone as well.

It is my understanding that heat shrink tool holders are reuseable. It would be a huge overkill for my purposes.

I don't need my tools to be perfectly on height on my mill so the Tormach system is also overkill.

I'm just curious about how much run-out folks get with their endmill holders.

 

[ChazzC]

How much do your tools run out in your end mill holders.

I honestly never checked, but I have found that different end mills fit better than others, so a slightly undersize shank will run out in the holder whereas it will run truer in a collet.

I'll do a quick check and update this post.


Update:

I wanted to do a fair comparison, so used a 1/2" holder & collet with a 1/2" dowel pin for the check: I have a 6" length of 0.495"/0.499" ground rod, but I also wanted to check one of my metric collets and didn't have any 12mm rround rod (but did have a 12mm dowel pin). Pins were held so that there was 1-1/2" stick-out and the measurements made 1" from the face of the holder/collet. I used a 0.0005" SHARS DTI held in a big Noga PH2040 solid arm base:

1/2" Dowel Pin

• 1/2" SHARS R-8 End Mill Holder: 0.0015" TIR
• 1/2" R-8 Collet: 0.003" TIR (maybe a speck of dirt, but I wiped the spindle & collets before the test)

12mm Dowel Pin

• 12mm R-8 Collet: 0.001" TIR

IIRC, the last time I checked the ID of my R-8 spindle its TIR was ~0.0005".

My R-8 collets are no-name off eBay, and the inch & metric were purchased years apart from different sellers; I think they were supposed to be 0.0006" — 0.0008" TIR. None of the current low-end sellers on eBay are listing TIR; $500 sets state 0.0004" TIR. On their website, SHARS has 0.0006" TIR "Precision" collets and 0.0005" TIR "High Precision" ones. No one (including SHARS) listed TIR for end mill holders, just "Precision Ground."

So I guess the answer is, "It depends:" get what fits for budget and needs (long reach or minimal stick-out).

 

[mksj]

End mill holders tend to stick out further from the spindle so the potential for increase TIR could occur, it is also a function of both the holder and the end mill. Another option is to go with an ER32 collet system and have several holders, which would probably cost similar to several decent end mill holder, and ER32 collet may have less stick out then an end mill holder. I also modified a 3/4" Iscar end mill holder for annular cutters and it is spot on as far as being able to measure any TIR. So maybe a function of the quality of the holder. Typically the specs for TIR on R8 collets can be 0.0006" or less, ER32 is about 2-3X less, at the end of the day for the purposes of end mill life use probably makes no difference in a hobbyist setting. In an industrial setting, increasing TIR does have a significant impact on tool life.

Personally, I do not like to use R8 collets, I find it difficult to get end mills in/out when using a power drawbar and the chance I get cut from the end mill is higher as well as holding it when pulling in the collet or ejecting it. I only use the R8 collets when I need high rigidity and the shortest stick out. If one uses a dial type of edge/center finder then TIR of the holder is a more significant issue. When I use an ER32 collet system I am usually within the 0.0002" spec., my dial edge finder repeats to 0.0004". It is not that I always need that level of accuracy, but just that the errors in run out can be compounded and that can cause you not hit your target sepcs. I am less worried about the impact on tool life, I usually drop the end mill and break a tooth before it wears out, or I do something stupid when milling.

 

[Batmanacw]

End mill holders tend to stick out further from the spindle so the potential for increase TIR could occur, it is also a function of both the holder and the end mill. Another option is to go with an ER32 collet system and have several holders, which would probably cost similar to several decent end mill holder, and ER32 collet may have less stick out then an end mill holder. I also modified a 3/4" Iscar end mill holder for annular cutters and it is spot on as far as being able to measure any TIR. So maybe a function of the quality of the holder. Typically the specs for TIR on R8 collets can be 0.0006" or less, ER32 is about 2-3X less, at the end of the day for the purposes of end mill life use probably makes no difference in a hobbyist setting. In an industrial setting, increasing TIR does have a significant impact on tool life.

Personally, I do not like to use R8 collets, I find it difficult to get end mills in/out when using a power drawbar and the chance I get cut from the end mill is higher as well as holding it when pulling in the collet or ejecting it. I only use the R8 collets when I need high rigidity and the shortest stick out. If one uses a dial type of edge/center finder then TIR of the holder is a more significant issue. When I use an ER32 collet system I am usually within the 0.0002" spec., my dial edge finder repeats to 0.0004". It is not that I always need that level of accuracy, but just that the errors in run out can be compounded and that can cause you not hit your target sepcs. I am less worried about the impact on tool life, I usually drop the end mill and break a tooth before it wears out, or I do something stupid when milling.

View attachment 431736

I have an ER40 collet chuck. It works fine but I'm looking to keep the over all length shorter which it is with endmill holders in 1/4, 3/8, and 1/2 sizes. I'm looking for real world information on what I can expect from a quality end mill holder.

My ER40 is not perfect but i typically see under 0.0005" tir. Using it means i cannot keep endmills set up all the time for quick change-outs. I'm not buying dozens of er40 collet chucks.