Fixture design. Not MC related

[JB7280]

A progressing position at work has me designing fixtures more, rather than just programming parts from already "engineered" fixtures, with leads me to some questions.  I'll start with this one, since I have thousands, when it comes to properly designing a fixture.  

 

Is there a general standard depth (#xD?) for slip/press fits of dowel pins used to position different pieces of the fixture?   Not for frequent on/off pieces like parts or subplates, but pieces of the fixture that are meant to be permanently assembled.    Thanks!

[crazy^millman]

1 hour ago, JB7280 said:

A progressing position at work has me designing fixtures more, rather than just programming parts from already "engineered" fixtures, with leads me to some questions.  I'll start with this one, since I have thousands, when it comes to properly designing a fixture.  

 

Is there a general standard depth (#xD?) for slip/press fits of dowel pins used to position different pieces of the fixture?   Not for frequent on/off pieces like parts or subplates, but pieces of the fixture that are meant to be permanently assembled.    Thanks!

.0002 TO .0005 for Steels was our rule of thumb for Dies. .001 to .0015 for Aluminum for press fit. I always did at least 1 to 1 if not 2 to 1 for dowel pins in steel and at least 2 to 1 or 3 to 1 for Aluminum. Keen Serts for Aluminum if production not a big fan of Helicoils. For one offs threaded aluminum was fine. Bigger is always better in my book. Stronger and supported will always make a good part. Weak and flimsy will always lead to issues. The balance is finding the right mix of strength and support. We switch over to Mill/Turns all bets are off. I have done and keep doing what at the time seems extremely crazy, but then it works and I try the next crazy thing. I have fixtures I made 2 decades ago still be used in different places I worked. 

[JB7280]

1 hour ago, 5th Axis CGI said:

.0002 TO .0005 for Steels was our rule of thumb for Dies. .001 to .0015 for Aluminum for press fit. I always did at least 1 to 1 if not 2 to 1 for dowel pins in steel and at least 2 to 1 or 3 to 1 for Aluminum. Keen Serts for Aluminum if production not a big fan of Helicoils. For one offs threaded aluminum was fine. Bigger is always better in my book. Stronger and supported will always make a good part. Weak and flimsy will always lead to issues. The balance is finding the right mix of strength and support. We switch over to Mill/Turns all bets are off. I have done and keep doing what at the time seems extremely crazy, but then it works and I try the next crazy thing. I have fixtures I made 2 decades ago still be used in different places I worked. 

I appreciate all of that info.  However, what I actually meant was the DEPTH of the pins.  Or is that what you meant by 1 to 1, 2 to 1, etc?  2xD?

[JoshC]

11 minutes ago, JB7280 said:

I appreciate all of that info.  However, what I actually meant was the DEPTH of the pins.  Or is that what you meant by 1 to 1, 2 to 1, etc?  2xD?

I think the formula shown below is what you might be looking for, this was from the machinery handbook and the formula they show here likely will give you what you need as long as you know how much force in tons that needs to be applied to the pins for press fit.

 

[crazy^millman]

1 hour ago, JB7280 said:

I appreciate all of that info.  However, what I actually meant was the DEPTH of the pins.  Or is that what you meant by 1 to 1, 2 to 1, etc?  2xD?

Yes that is what I meant. 1 to 1 depth so 1 times deep by 1 times the diameter of the pin. 1/2 pin would have 1/2 of reamed hole depth minimum. I like 1 to 1-1/2 or 1 to 2 when I have that option in steel. Aluminum is just normally 2 to 1 and good enough. 

[mayday]

just remember dowel pins are for position, not lateral holding force, use keys for that

[Guest]

Maybe jigs and fixtures are your thing, I made a thermoforming jig in a rush for curving microlumber edges for a Global 5000 Conference table, ended up looking like a klingon Bat'leth when I was done.(It did work)  I would post a picture of it if I could.

[Guest]

One thing that makes designing jigs in mastercam so great is the model prep features like move and push and pull. 

[JParis]

6 hours ago, JB7280 said:

A progressing position at work has me designing fixtures more, rather than just programming parts from already "engineered" fixtures, with leads me to some questions.  I'll start with this one, since I have thousands, when it comes to properly designing a fixture.  

 

Is there a general standard depth (#xD?) for slip/press fits of dowel pins used to position different pieces of the fixture?   Not for frequent on/off pieces like parts or subplates, but pieces of the fixture that are meant to be permanently assembled.    Thanks!

Ultimately, I think this comes down to what are you trying to build a fixture to achieve?  Assembly, Manufacturing, Tooling..they can all have slightly different requirements and needs.

Many of my production fixtures are made out of aluminum, however the location and hard location points are always steel....the variety varies but as they mostly in coolant working with something that is non-corrosive factors into the thought process. When designing I always prefer the KISS theory. I don't like to design what I refer to as an "erector set". I prefer hard location points and reliable clamping.

I don't typically use dowels but on occasion if I do, I typically, when mounting in aluminum use a 2:1 ratio,,,,.250 pin, x .500 deep....I will relieve the top of the hole(.0002/.0004") so it's not a press fit for the entire .500 depth and it also starts the pin straight.  If I am creating a fixture that utilizes removable locators that allow a part to be loaded off the machine, I then rely on diamond and bullet nose pins and sleeves for achieving location. I always try to use off the shelf clamping, though it's not always correct for out parts, so we do make some....hard fixtures, I make from steel....

When mounting threaded clamps that will be cycled tight/loose thousands of times, I generally use EZ-Loks...I frown upon Heli-coils for longevity.

Press fit stock will vary by size, on something small I might go with a .0003/.0005" press, something larger that will increase the stock to leave for press by a few .0001"'s

I always try to remember, if I need to hold .001 true position, my fixture needs to be within .0003".....

Machinery's Handbook can provide some good starting values for things...

HTH

Here's just a few of the tombstones I've done fairly recently

 

 

The cage has become popular in the shop because of the ease of loading stock and the fact the part comes off complete just needing to be broken out and edge cleaned. The operators don't have to worry about a ton and tight side to side tolerance stay put.

 

[JB7280]

50 minutes ago, content creator said:

One thing that makes designing jigs in mastercam so great is the model prep features like move and push and pull. 

I'm actually making the models for them in Solidworks.  These are just for assembly of the machining fixture. I just want to start off with good habits.

 

Thanks for all the responses.

[Guest]

1 minute ago, JB7280 said:

I'm actually making the models for them in Solidworks.  These are just for assembly of the machining fixture. I just want to start off with good habits.

 

Thanks for all the responses.

Oh cool, I've never actually used solidworks. But I have a coworker who can't stop telling me how good it is, since 2 years xD

[JB7280]

1 minute ago, content creator said:

Oh cool, I've never actually used solidworks. But I have a coworker who can't stop telling me how good it is, since 2 years xD

It's nice, but it's definitely easy to get yourself into trouble.  If your assemblies aren't well planned in the beginning, it can bite you in the xxxx later.  At least for me it does.

[JParis]

Just now, JB7280 said:

It's nice, but it's definitely easy to get yourself into trouble.  If your assemblies aren't well planned in the beginning, it can bite you in the xxxx later.  At least for me it does.

In SW's, if your parts are designed well, assemblies "should" be a snap....I'd be curious about the issue you run into...

[JB7280]

3 minutes ago, JParis said:

In SW's, if your parts are designed well, assemblies "should" be a snap....I'd be curious about the issue you run into...

Inexperience, and no formal training is the real issue.  I find myself going back to fix broken mates semi-frequently.  I used SW at an old shop, but only just got a license here.  My main issue has been finding ways to mate things correctly, where to use reference planes, etc.  And things becoming "broken" when I go back to modify something that I change my mind on.  

 

Again, I blame 90% of it on inexperience.

[JParis]

1 minute ago, JB7280 said:

Again, I blame 90% of it on inexperience.

Realistically, that's probably a fair assessment. 

When I am designing, I will always try to add those features at the part level, so that when I do start the assembly process, that stuff is readily available...so during the design process, I am considering what my end game is going to be at that time.

[Guest]

You know, having never used a cad software like sw I can't speak to it's advantages or disadvantages, however I know when the bigshots at my company want something like a solid sliced into layers or a quick jig they usually want it done in mc by a programmer. Which kinds of makes me question if sw is helping you more than hinder you?

[JParis]

3 minutes ago, content creator said:

You know, having never used a cad software like sw I can't speak to it's advantages or disadvantages, however I know when the bigshots at my company want something like a solid sliced into layers or a quick jig they usually want it done in mc by a programmer. Which kinds of makes me question if sw is helping you more than hinder you?

SW's CAD functionality is eons beyond MCAM...SW's is a true CAD design package

Though I will admit, MCAM is making strides, it is still a CAM software with some CAD ability

[Guest]

Yes Mastercam does not have all the bells and whistles of softwares like sw or Catia, although I must say catia always feels like a clunky old dinosaur to me, but I know just like anything else just takes getting used to.

[JB7280]

8 minutes ago, content creator said:

You know, having never used a cad software like sw I can't speak to it's advantages or disadvantages, however I know when the bigshots at my company want something like a solid sliced into layers or a quick jig they usually want it done in mc by a programmer. Which kinds of makes me question if sw is helping you more than hinder you?

Solidworks is pretty amazing when used right.  The part I like, is being able to make professional prints from your model.  I haven't been able to get a good print out of MC.  Prints are becoming useful because our machines are all full of parts, so we're having to have fixtures farmed out.

[JB7280]

7 minutes ago, JParis said:

SW's CAD functionality is eons beyond MCAM...SW's is a true CAD design package

Though I will admit, MCAM is making strides, it is still a CAM software with some CAD ability

I loved Esprit, and prefer it over Mastercam, as far as the CAM side goes.  But I have to say, Mastercam has impressive CAD abilities, in comparison.

[Guest]

For me what makes me a big mc fan is the open api so I can do mods then kick back and click some buttons then go home. I know poor work ethic but I worked hard in my life so when I can take shortcuts I take em.

[Guest]

Been thinking of doing some design based macros for doing stuff like making fixtures and what not. 

[JB7280]

4 minutes ago, content creator said:

For me what makes me a big mc fan is the open api so I can do mods then kick back and click some buttons then go home. I know poor work ethic but I worked hard in my life so when I can take shortcuts I take em.

I believe Esprit had lots of things that could be done with api as well.  But I'm not nearly the power users that you guys are.  I love the official, machine builder certified posts in Esprit, the direct support (no reseller), and to me, the plane/wcs system was easier.  But Esprit is also the first CAM software I learned to program with.  I hated MC at first.  It ain't bad now though, and it's what I've got, so I'm learning to like it. 

[Guest]

Esprit sounds interesting, and yeah mc grows on you, I first learned mc in school back in 2008 been using it on and off since then, but there is sooo much to learn most of the users on here are eons ahead of me

[JParis]

The bottom line, any tool is only as good as the hands of the craftsman are that utilize it