Blind, Threaded Hole - How can I Eliminate Chips?

[Tom Slack]

Connie,
I wish I say that I have had the exact same problem, but I can't. The closest I've come to it was when I was on a project for decreasing specks on motion picture film created during slitting. (Since then, I've never been able to watch a movie without looking at the edge of the screen for specks.)

First a really stupid question, How does the customer know when they have a burr problem? How do they define a burr? On a microscopic scale, all metal parts have burrs.

Once you have defined the problem, do the textbook things, do attribute control charts, take the results of the problem solving sessions and do a designed experiment (for attributes). During this, keep the customer in the loop ofcourse.

I realize this advice is as dull as dirt, but it always works.

Best Wishes,

Tom

 

[mshell]

You did mention that is was a threaded screw. I am just not familiar with the screw manufacturing process. Good luck with your problem. I hope you resolve the issue soon.

 

[Craig H.]

The Debris is caused by the threading tool I guess I forgot to mention that it is a threaded hole.

Connie:

At the risk of sounding stupid (won't be the first) is the material magnetic? If so, maybe rapping the part on a magnet (covered with something that can be removed and cleaned) would jar the shards loose?

Just a thought.

Craig

 

[Govind]

Hi Everyone It's Been A Long Time But We Have Been Very Busy.

I Have A Question (not Sure Where To Post It Though) About A Part That Has Been Driving Us Nuts For Quite Some Time, So Any Help Will Be Greatly Appretiated!!!!

Here It Is:

We Make A Few Parts That Have A Blind Threaded Hole, Our Customer Tells Us That They Cannot Have Any Debris Or Chips In The Holes, Now We Have Tried Everything We Can Possibly Think Of To Eliminate This Issue, We Used Chip Breaking Tools Which Have Helped Some To Eliminate The Larger Chips, We Have Put Parts Immediatly In Solvent To Release Any Oils That May Be Making The Chips Hang In There, We Have Tried Vibration Washing None Of Which Eliminates This 100% Which Is What The Customer Wants.

These Are Run On A Five Spindle Davenport Screw Machine.

If Anyone Else Runs This Type Of Part And Has Been Successful At Eliminating The Chips Please Let Me Know How You Do It!!!

Thannk-you!!!!
Connie

Also Where Is The Spell Check???

Connie,
I would look into the calculation of Core hole (minor diameter) of the thread and also the condition of the threading tool.

Besides; thinking out loud..
Is the selection of the tool correct? Interms of rake angles?
Is the tool overhang too much?
Is there a vibration in the machine?
Backlash in the machine lead screw too much?
Is part adequately held in the chuck with uniform pressure?

I guess there should be deburring tool in the market to remove such burrs. You may want to use a magnetic core to attract the burr after deburr has fallen into the blind end? (assuming ferrous).

If you plan to use water, keep in mind the condensed water may settle in the blind hole and form rust. I would suggest you use low viscous oil to clean up the burr instead water.

Keep us posted if you find a better way.

Govind.

 

[Wes Bucey]

Hi Everyone It's Been A Long Time But We Have Been Very Busy.

I Have A Question (not Sure Where To Post It Though) About A Part That Has Been Driving Us Nuts For Quite Some Time, So Any Help Will Be Greatly Appretiated!!!!

Here It Is:

We Make A Few Parts That Have A Blind Threaded Hole, Our Customer Tells Us That They Cannot Have Any Debris Or Chips In The Holes, Now We Have Tried Everything We Can Possibly Think Of To Eliminate This Issue, We Used Chip Breaking Tools Which Have Helped Some To Eliminate The Larger Chips, We Have Put Parts Immediatly In Solvent To Release Any Oils That May Be Making The Chips Hang In There, We Have Tried Vibration Washing None Of Which Eliminates This 100% Which Is What The Customer Wants.

These Are Run On A Five Spindle Davenport Screw Machine.

If Anyone Else Runs This Type Of Part And Has Been Successful At Eliminating The Chips Please Let Me Know How You Do It!!!

Thannk-you!!!!
Connie

Also Where Is The Spell Check???

This is a common problem in machining blind threaded holes.

Often, it requires concurrent engineering with the customer to completely eliminate the problem.

Cause:
As the threading tool cuts a female thread in a smooth hole it pushes metal chips toward the blind end (regardless of the gravitational orientation of the hole - up, down, sideways.) The chips accumulate in the blind end of the hole because the thread cutting tool doesn't go all the way to the blind end. Often, in the threading operation, the chips don't break into tiny pieces but are longer pieces of "wire" which are springy and won't flush out of the hole.

Typical cure:
the main cure is to assure the chips are broken and tiny enough to be flushed out. The primary method is to make a "relief cut" at the end of the blind hole between the bottom and the last thread which breaks up any thread "curl" into small chips and allows the debris to be washed out. This requires design allowance for this final tooling operation. There are tool heads which work on a cam action to throw a blade out when pressure is applied to the shoulder of the tool at the face of the hole (limited to larger diameters) - the value is that the threads are never touched by the tool, only the chips in the path of the relief cut. Alternately, a much smaller diameter tool is fed into the hole past the thread and run like an orbital sander to cut the relief groove in the space between the end of the blind hole and the last thread. There is also
a "thread chaser" which follows the thread profile and breaks the chips into tiny pieces which can be flushed out.

Note: cleaning all chips out is especially important when dealing with certain applications where the male screw going into the female thread may break up the thread curls and allow them to fall back out into the assembly when the screw is removed for maintenance, contaminating the assembly and causing potential hazards (short circuits, dropping into food or cosmetics, etc.) Another hazard is possible prevention of completing assembly because the screw can't be put in all the way.

Bottom line: This is a joint problem of machinist and customer and needs attention.

 

[Proud Liberal]

Have you tried half-round drills followed with a cleaning operation in a ultrasonic water bath? We do that on holes as small as .023" with good success.

 

[Bob Ablondi]

Hi Everyone It's Been A Long Time But We Have Been Very Busy.

I Have A Question (not Sure Where To Post It Though) About A Part That Has Been Driving Us Nuts For Quite Some Time, So Any Help Will Be Greatly Appretiated!!!!

Here It Is:

We Make A Few Parts That Have A Blind Threaded Hole, Our Customer Tells Us That They Cannot Have Any Debris Or Chips In The Holes, Now We Have Tried Everything We Can Possibly Think Of To Eliminate This Issue, We Used Chip Breaking Tools Which Have Helped Some To Eliminate The Larger Chips, We Have Put Parts Immediatly In Solvent To Release Any Oils That May Be Making The Chips Hang In There, We Have Tried Vibration Washing None Of Which Eliminates This 100% Which Is What The Customer Wants.

These Are Run On A Five Spindle Davenport Screw Machine.

If Anyone Else Runs This Type Of Part And Has Been Successful At Eliminating The Chips Please Let Me Know How You Do It!!!

Thannk-you!!!!
Connie

Also Where Is The Spell Check???

If your company belongs to the PMPA, they have a forum similir to the Cove. On company manufactures a unit that uses a compination of ndt methods to identify debris. chips in the ID of parts. Ford Motor uses this company to sort theirparts.

 

[cbehrens]

How about trying a thread forming tap instead of a thread cutting tap. They produce no chips!!

 

[AllanJ]

Since Connie made the original post for this problem July 7 last year and has not repeated her request for a solution perhaps one might assume her poor blind threaded hole has been relieved of unwanted debris.

A happy ending, indeed.

 

[Wes Bucey]

How about trying a thread forming tap instead of a thread cutting tap. They produce no chips!!

True, but efficacy of process depends on material and what happens with displacement of material and whether the material is cold worked to change hardness. Tool bits can have thread chasers, etc. to clear out a lot of debris. One technique we used on some occasions was to use a secondary tool (like a milling cutter) which went into the bottom of the threaded hole and cut a flat bottom "relief channel" to clean out the accumulated debris from the thread cutting process.